
<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8866: SDP: Session Description Protocol</title>
<meta content="Ali Begen" name="author">
<meta content="Paul Kyzivat" name="author">
<meta content="Colin Perkins" name="author">
<meta content="Mark Handley" name="author">
<meta content="
       This memo defines the Session Description Protocol (SDP). SDP is
      intended for describing multimedia sessions for the purposes of session
      announcement, session invitation, and other forms of multimedia session
      initiation. This document obsoletes RFC 4566. 
    " name="description">
<meta content="xml2rfc 3.5.0" name="generator">
<meta content="Multimedia" name="keyword">
<meta content="conferencing" name="keyword">
<meta content="session setup" name="keyword">
<meta content="signaling" name="keyword">
<meta content="media" name="keyword">
<meta content="SIP" name="keyword">
<meta content="RTSP" name="keyword">
<meta content="voip" name="keyword">
<meta content="audio" name="keyword">
<meta content="video" name="keyword">
<meta content="streaming" name="keyword">
<meta content="8866" name="rfc.number">
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    appdirs 1.4.4
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    google-i18n-address 2.3.5
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<link href="rfc8866.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
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  font-weight: bold;
  line-height: 1.3;
}
#title {
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  border-bottom: 1px solid #ddd;
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  padding: 1em 0 0.5em;
}
.author {
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}
h1 {
  font-size: 26px;
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}
h2 {
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h3 {
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h4 {
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h5, h6 {
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#n-copyright-notice {
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/* general structure */
p {
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div, span {
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div {
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.alignRight.art-text pre {
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.alignRight {
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.alignRight > *:first-child {
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}
.alignRight > *:nth-child(2) {
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svg {
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.alignCenter.art-text pre {
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.alignCenter {
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.alignCenter > *:first-child {
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  */
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}

/* lists */
ol, ul {
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  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
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}
li {
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.ulCompact li {
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ul.empty, .ulEmpty {
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ul.empty li, .ulEmpty li {
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ul.compact, .ulCompact,
ol.compact, .olCompact {
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  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
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}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
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}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre, code {
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  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
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}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
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/* aside, blockquote */
aside, blockquote {
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  padding: 1.2em 2em;
}
blockquote {
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  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
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  margin: 1em 0;
}
cite {
  display: block;
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  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
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th {
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tr:nth-child(2n+1) > td {
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table caption {
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}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
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}

/* pilcrow */
a.pilcrow {
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@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
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  a.pilcrow:hover {
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}

/* misc */
hr {
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  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
#identifiers .authors .author {
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  margin-right: 1.5em;
}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
  float: left;
}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
    -moz-column-gap: 0;
  }
}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
  margin: 0.5em 0;
}
address.vcard .type {
  display: none;
}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
  position: absolute;
  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
  }
  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
  }
  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
    padding: 0.25em 1em 1em 0;
  }
  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
  }
  p {
    orphans: 3;
    widows: 3;
  }
  #n-copyright-notice {
    border-bottom: none;
  }
  #toc, #n-introduction {
    page-break-before: always;
  }
  #toc {
    border-top: none;
    padding-top: 0;
  }
  figure, pre {
    page-break-inside: avoid;
  }
  figure {
    overflow: scroll;
  }
  h1, h2, h3, h4, h5, h6 {
    page-break-after: avoid;
  }
  h2+*, h3+*, h4+*, h5+*, h6+* {
    page-break-before: avoid;
  }
  pre {
    white-space: pre-wrap;
    word-wrap: break-word;
    font-size: 10pt;
  }
  table {
    border: 1px solid #ddd;
  }
  td {
    border-top: 1px solid #ddd;
  }
}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
.ears thead .left {
  string-set: ears-top-left content();
}

.ears thead .center {
  string-set: ears-top-center content();
}

.ears thead .right {
  string-set: ears-top-right content();
}

.ears tfoot .left {
  string-set: ears-bottom-left content();
}

.ears tfoot .center {
  string-set: ears-bottom-center content();
}

.ears tfoot .right {
  string-set: ears-bottom-right content();
}
*/

@page :first {
  padding-top: 0;
  @top-left {
    content: normal;
    border: none;
  }
  @top-center {
    content: normal;
    border: none;
  }
  @top-right {
    content: normal;
    border: none;
  }
}

@page {
  size: A4;
  margin-bottom: 45mm;
  padding-top: 20px;
  /* The follwing is commented out here, but set appropriately by in code, as
     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-left {
    content: string(ears-top-left);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-center {
    content: string(ears-top-center);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-right {
    content: string(ears-top-right);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @bottom-left {
    content: string(ears-bottom-left);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-center {
    content: string(ears-bottom-center);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-right {
      content: '[Page ' counter(page) ']';
      vertical-align: top;
      border-top: solid 1px #ccc;
  }
  */

}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
  width: 8em;
}

/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
  #toc a.toplink,
  #toc a.toplink:hover {
    color: white;
    background-color: #444;
    text-decoration: none;
  }
}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
    padding: 0 0 1em 1em;
  }
}

/* Style section numbers with more space between number and title */
.section-number {
  padding-right: 0.5em;
}

/* prevent monospace from becoming overly large */
tt, code, pre, code {
  font-size: 95%;
}

/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
.art-text pre {
  line-height: 1.12;
}


/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
  float: right;
  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
  text-align: left;
}
table td.text-center,
table th.text-center {
  text-align: center;
}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact informatio look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
  width: auto;
}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
    padding-top: 1px;
  }

  /* Avoid page breaks inside dl and author address entries */
  .vcard {
    page-break-inside: avoid;
  }

}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
  font-variant: small-caps;
  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
  margin: 1em 0 0 0;
}
/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
   possibly even requiring a new line */
@media print {
  a.pilcrow {
    display: none;
  }
}
/* Styling for the external metadata */
div#external-metadata {
  background-color: #eee;
  padding: 0.5em;
  margin-bottom: 0.5em;
  display: none;
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<link href="https://dx.doi.org/10.17487/rfc8866" rel="alternate">
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<table class="ears">
<thead><tr>
<td class="left">RFC 8866</td>
<td class="center">SDP</td>
<td class="right">January 2021</td>
</tr></thead>
<tfoot><tr>
<td class="left">Begen, et al.</td>
<td class="center">Standards Track</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc8866" class="eref">8866</a></dd>
<dt class="label-obsoletes">Obsoletes:</dt>
<dd class="obsoletes">
<a href="https://www.rfc-editor.org/rfc/rfc4566" class="eref">4566</a> </dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2021-01" class="published">January 2021</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">A. Begen</div>
<div class="org">Networked Media</div>
</div>
<div class="author">
      <div class="author-name">P. Kyzivat</div>
</div>
<div class="author">
      <div class="author-name">C. Perkins</div>
<div class="org">University of Glasgow</div>
</div>
<div class="author">
      <div class="author-name">M. Handley</div>
<div class="org">UCL</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8866</h1>
<h1 id="title">SDP: Session Description Protocol</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">This memo defines the Session Description Protocol (SDP). SDP is
      intended for describing multimedia sessions for the purposes of session
      announcement, session invitation, and other forms of multimedia session
      initiation. This document obsoletes RFC 4566.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This is an Internet Standards Track document.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc8866">https://www.rfc-editor.org/info/rfc8866</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
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            This document is subject to BCP 78 and the IETF Trust's Legal
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</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1" class="keepWithNext"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1" class="keepWithNext"><a href="#section-2" class="xref">2</a>.  <a href="#name-glossary-of-terms" class="xref">Glossary of Terms</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-examples-of-sdp-usage" class="xref">Examples of SDP Usage</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.3.2.1">
                <p id="section-toc.1-1.3.2.1.1" class="keepWithNext"><a href="#section-3.1" class="xref">3.1</a>.  <a href="#name-session-initiation" class="xref">Session Initiation</a><a href="#section-toc.1-1.3.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.3.2.2">
                <p id="section-toc.1-1.3.2.2.1"><a href="#section-3.2" class="xref">3.2</a>.  <a href="#name-streaming-media" class="xref">Streaming Media</a><a href="#section-toc.1-1.3.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.3.2.3">
                <p id="section-toc.1-1.3.2.3.1"><a href="#section-3.3" class="xref">3.3</a>.  <a href="#name-email-and-the-world-wide-we" class="xref">Email and the World Wide Web</a><a href="#section-toc.1-1.3.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.3.2.4">
                <p id="section-toc.1-1.3.2.4.1"><a href="#section-3.4" class="xref">3.4</a>.  <a href="#name-multicast-session-announcem" class="xref">Multicast Session Announcement</a><a href="#section-toc.1-1.3.2.4.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-requirements-and-recommenda" class="xref">Requirements and Recommendations</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.4.2.1">
                <p id="section-toc.1-1.4.2.1.1"><a href="#section-4.1" class="xref">4.1</a>.  <a href="#name-media-and-transport-informa" class="xref">Media and Transport Information</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.4.2.2">
                <p id="section-toc.1-1.4.2.2.1"><a href="#section-4.2" class="xref">4.2</a>.  <a href="#name-timing-information" class="xref">Timing Information</a><a href="#section-toc.1-1.4.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.4.2.3">
                <p id="section-toc.1-1.4.2.3.1"><a href="#section-4.3" class="xref">4.3</a>.  <a href="#name-obtaining-further-informati" class="xref">Obtaining Further Information about a Session</a><a href="#section-toc.1-1.4.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.4.2.4">
                <p id="section-toc.1-1.4.2.4.1"><a href="#section-4.4" class="xref">4.4</a>.  <a href="#name-internationalization" class="xref">Internationalization</a><a href="#section-toc.1-1.4.2.4.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-sdp-specification" class="xref">SDP Specification</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.5.2.1">
                <p id="section-toc.1-1.5.2.1.1"><a href="#section-5.1" class="xref">5.1</a>.  <a href="#name-protocol-version-v" class="xref">Protocol Version ("v=")</a><a href="#section-toc.1-1.5.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.2">
                <p id="section-toc.1-1.5.2.2.1"><a href="#section-5.2" class="xref">5.2</a>.  <a href="#name-origin-o" class="xref">Origin ("o=")</a><a href="#section-toc.1-1.5.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.3">
                <p id="section-toc.1-1.5.2.3.1"><a href="#section-5.3" class="xref">5.3</a>.  <a href="#name-session-name-s" class="xref">Session Name ("s=")</a><a href="#section-toc.1-1.5.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.4">
                <p id="section-toc.1-1.5.2.4.1"><a href="#section-5.4" class="xref">5.4</a>.  <a href="#name-session-information-i" class="xref">Session Information ("i=")</a><a href="#section-toc.1-1.5.2.4.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.5">
                <p id="section-toc.1-1.5.2.5.1"><a href="#section-5.5" class="xref">5.5</a>.  <a href="#name-uri-u" class="xref">URI ("u=")</a><a href="#section-toc.1-1.5.2.5.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.6">
                <p id="section-toc.1-1.5.2.6.1"><a href="#section-5.6" class="xref">5.6</a>.  <a href="#name-email-address-and-phone-num" class="xref">Email Address and Phone Number ("e=" and "p=")</a><a href="#section-toc.1-1.5.2.6.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.7">
                <p id="section-toc.1-1.5.2.7.1"><a href="#section-5.7" class="xref">5.7</a>.  <a href="#name-connection-information-c" class="xref">Connection Information ("c=")</a><a href="#section-toc.1-1.5.2.7.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.8">
                <p id="section-toc.1-1.5.2.8.1"><a href="#section-5.8" class="xref">5.8</a>.  <a href="#name-bandwidth-information-b" class="xref">Bandwidth Information ("b=")</a><a href="#section-toc.1-1.5.2.8.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.9">
                <p id="section-toc.1-1.5.2.9.1"><a href="#section-5.9" class="xref">5.9</a>.  <a href="#name-time-active-t" class="xref">Time Active ("t=")</a><a href="#section-toc.1-1.5.2.9.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.10">
                <p id="section-toc.1-1.5.2.10.1"><a href="#section-5.10" class="xref">5.10</a>. <a href="#name-repeat-times-r" class="xref">Repeat Times ("r=")</a><a href="#section-toc.1-1.5.2.10.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.11">
                <p id="section-toc.1-1.5.2.11.1"><a href="#section-5.11" class="xref">5.11</a>. <a href="#name-time-zone-adjustment-z" class="xref">Time Zone Adjustment ("z=")</a><a href="#section-toc.1-1.5.2.11.1" class="pilcrow">¶</a></p>
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              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.12">
                <p id="section-toc.1-1.5.2.12.1"><a href="#section-5.12" class="xref">5.12</a>. <a href="#name-encryption-keys-k" class="xref">Encryption Keys ("k=")</a><a href="#section-toc.1-1.5.2.12.1" class="pilcrow">¶</a></p>
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              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.13">
                <p id="section-toc.1-1.5.2.13.1"><a href="#section-5.13" class="xref">5.13</a>. <a href="#name-attributes-a" class="xref">Attributes ("a=")</a><a href="#section-toc.1-1.5.2.13.1" class="pilcrow">¶</a></p>
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              <li class="compact ulEmpty toc" id="section-toc.1-1.5.2.14">
                <p id="section-toc.1-1.5.2.14.1"><a href="#section-5.14" class="xref">5.14</a>. <a href="#name-media-descriptions-m" class="xref">Media Descriptions ("m=")</a><a href="#section-toc.1-1.5.2.14.1" class="pilcrow">¶</a></p>
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          <li class="compact ulEmpty toc" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-sdp-attributes" class="xref">SDP Attributes</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-cat-category" class="xref">cat (Category)</a><a href="#section-toc.1-1.6.2.1.1" class="pilcrow">¶</a></p>
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              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-keywds-keywords" class="xref">keywds (Keywords)</a><a href="#section-toc.1-1.6.2.2.1" class="pilcrow">¶</a></p>
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                <p id="section-toc.1-1.6.2.3.1"><a href="#section-6.3" class="xref">6.3</a>.  <a href="#name-tool" class="xref">tool</a><a href="#section-toc.1-1.6.2.3.1" class="pilcrow">¶</a></p>
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                <p id="section-toc.1-1.6.2.4.1"><a href="#section-6.4" class="xref">6.4</a>.  <a href="#name-ptime-packet-time" class="xref">ptime (Packet Time)</a><a href="#section-toc.1-1.6.2.4.1" class="pilcrow">¶</a></p>
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              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.5">
                <p id="section-toc.1-1.6.2.5.1"><a href="#section-6.5" class="xref">6.5</a>.  <a href="#name-maxptime-maximum-packet-tim" class="xref">maxptime (Maximum Packet Time)</a><a href="#section-toc.1-1.6.2.5.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.6">
                <p id="section-toc.1-1.6.2.6.1"><a href="#section-6.6" class="xref">6.6</a>.  <a href="#name-rtpmap" class="xref">rtpmap</a><a href="#section-toc.1-1.6.2.6.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.7">
                <p id="section-toc.1-1.6.2.7.1"><a href="#section-6.7" class="xref">6.7</a>.  <a href="#name-media-direction-attributes" class="xref">Media Direction Attributes</a><a href="#section-toc.1-1.6.2.7.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.6.2.7.2.1">
                    <p id="section-toc.1-1.6.2.7.2.1.1"><a href="#section-6.7.1" class="xref">6.7.1</a>.  <a href="#name-recvonly-receive-only" class="xref">recvonly (Receive-Only)</a><a href="#section-toc.1-1.6.2.7.2.1.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.7.2.2">
                    <p id="section-toc.1-1.6.2.7.2.2.1"><a href="#section-6.7.2" class="xref">6.7.2</a>.  <a href="#name-sendrecv-send-receive" class="xref">sendrecv (Send-Receive)</a><a href="#section-toc.1-1.6.2.7.2.2.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.7.2.3">
                    <p id="section-toc.1-1.6.2.7.2.3.1"><a href="#section-6.7.3" class="xref">6.7.3</a>.  <a href="#name-sendonly-send-only" class="xref">sendonly (Send-Only)</a><a href="#section-toc.1-1.6.2.7.2.3.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.7.2.4">
                    <p id="section-toc.1-1.6.2.7.2.4.1"><a href="#section-6.7.4" class="xref">6.7.4</a>.  <a href="#name-inactive" class="xref">inactive</a><a href="#section-toc.1-1.6.2.7.2.4.1" class="pilcrow">¶</a></p>
</li>
                </ul>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.8">
                <p id="section-toc.1-1.6.2.8.1"><a href="#section-6.8" class="xref">6.8</a>.  <a href="#name-orient-orientation" class="xref">orient (Orientation)</a><a href="#section-toc.1-1.6.2.8.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.9">
                <p id="section-toc.1-1.6.2.9.1"><a href="#section-6.9" class="xref">6.9</a>.  <a href="#name-type-conference-type" class="xref">type (Conference Type)</a><a href="#section-toc.1-1.6.2.9.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.10">
                <p id="section-toc.1-1.6.2.10.1"><a href="#section-6.10" class="xref">6.10</a>. <a href="#name-charset-character-set" class="xref">charset (Character Set)</a><a href="#section-toc.1-1.6.2.10.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.11">
                <p id="section-toc.1-1.6.2.11.1"><a href="#section-6.11" class="xref">6.11</a>. <a href="#name-sdplang-sdp-language" class="xref">sdplang (SDP Language)</a><a href="#section-toc.1-1.6.2.11.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.12">
                <p id="section-toc.1-1.6.2.12.1"><a href="#section-6.12" class="xref">6.12</a>. <a href="#name-lang-language" class="xref">lang (Language)</a><a href="#section-toc.1-1.6.2.12.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.13">
                <p id="section-toc.1-1.6.2.13.1"><a href="#section-6.13" class="xref">6.13</a>. <a href="#name-framerate-frame-rate" class="xref">framerate (Frame Rate)</a><a href="#section-toc.1-1.6.2.13.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.14">
                <p id="section-toc.1-1.6.2.14.1"><a href="#section-6.14" class="xref">6.14</a>. <a href="#name-quality" class="xref">quality</a><a href="#section-toc.1-1.6.2.14.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.15">
                <p id="section-toc.1-1.6.2.15.1"><a href="#section-6.15" class="xref">6.15</a>. <a href="#name-fmtp-format-parameters" class="xref">fmtp (Format Parameters)</a><a href="#section-toc.1-1.6.2.15.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="xref">8</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.8.2.1">
                <p id="section-toc.1-1.8.2.1.1"><a href="#section-8.1" class="xref">8.1</a>.  <a href="#name-the-application-sdp-media-t" class="xref">The "application/sdp" Media Type</a><a href="#section-toc.1-1.8.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2">
                <p id="section-toc.1-1.8.2.2.1"><a href="#section-8.2" class="xref">8.2</a>.  <a href="#name-registration-of-sdp-paramet" class="xref">Registration of SDP Parameters with IANA</a><a href="#section-toc.1-1.8.2.2.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.1">
                    <p id="section-toc.1-1.8.2.2.2.1.1"><a href="#section-8.2.1" class="xref">8.2.1</a>.  <a href="#name-registration-procedure" class="xref">Registration Procedure</a><a href="#section-toc.1-1.8.2.2.2.1.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.2">
                    <p id="section-toc.1-1.8.2.2.2.2.1"><a href="#section-8.2.2" class="xref">8.2.2</a>.  <a href="#name-media-types-media" class="xref">Media Types (&lt;media&gt;)</a><a href="#section-toc.1-1.8.2.2.2.2.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.3">
                    <p id="section-toc.1-1.8.2.2.2.3.1"><a href="#section-8.2.3" class="xref">8.2.3</a>.  <a href="#name-transport-protocols-proto" class="xref">Transport Protocols (&lt;proto&gt;)</a><a href="#section-toc.1-1.8.2.2.2.3.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.4">
                    <p id="section-toc.1-1.8.2.2.2.4.1"><a href="#section-8.2.4" class="xref">8.2.4</a>.  <a href="#name-attribute-names-attribute-n" class="xref">Attribute Names (&lt;attribute-name&gt;)</a><a href="#section-toc.1-1.8.2.2.2.4.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.5">
                    <p id="section-toc.1-1.8.2.2.2.5.1"><a href="#section-8.2.5" class="xref">8.2.5</a>.  <a href="#name-bandwidth-specifiers-bwtype" class="xref">Bandwidth Specifiers (&lt;bwtype&gt;)</a><a href="#section-toc.1-1.8.2.2.2.5.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.6">
                    <p id="section-toc.1-1.8.2.2.2.6.1"><a href="#section-8.2.6" class="xref">8.2.6</a>.  <a href="#name-network-types-nettype" class="xref">Network Types (&lt;nettype&gt;)</a><a href="#section-toc.1-1.8.2.2.2.6.1" class="pilcrow">¶</a></p>
</li>
                  <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.2.2.7">
                    <p id="section-toc.1-1.8.2.2.2.7.1"><a href="#section-8.2.7" class="xref">8.2.7</a>.  <a href="#name-address-types-addrtype" class="xref">Address Types (&lt;addrtype&gt;)</a><a href="#section-toc.1-1.8.2.2.2.7.1" class="pilcrow">¶</a></p>
</li>
                </ul>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.8.2.3">
                <p id="section-toc.1-1.8.2.3.1"><a href="#section-8.3" class="xref">8.3</a>.  <a href="#name-encryption-key-access-metho" class="xref">Encryption Key Access Methods (OBSOLETE)</a><a href="#section-toc.1-1.8.2.3.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-9" class="xref">9</a>.  <a href="#name-sdp-grammar" class="xref">SDP Grammar</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-10" class="xref">10</a>. <a href="#name-summary-of-changes-from-rfc" class="xref">Summary of Changes from RFC 4566</a><a href="#section-toc.1-1.10.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#section-11" class="xref">11</a>. <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.11.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.11.2.1">
                <p id="section-toc.1-1.11.2.1.1"><a href="#section-11.1" class="xref">11.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.11.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.11.2.2">
                <p id="section-toc.1-1.11.2.2.1"><a href="#section-11.2" class="xref">11.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.11.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.12">
            <p id="section-toc.1-1.12.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.12.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.13">
            <p id="section-toc.1-1.13.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.13.1" class="pilcrow">¶</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">When initiating multimedia teleconferences, voice-over-IP calls,
      streaming video, or other sessions, there is a requirement to convey
      media details, transport addresses, and other session description
      metadata to the participants.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">SDP provides a standard representation for such information,
      irrespective of how that information is transported. SDP is purely a
      format for session description -- it does not incorporate a transport
      protocol, and it is intended to use different transport protocols as
      appropriate, including the Session Announcement Protocol (SAP) <span>[<a href="#RFC2974" class="xref">RFC2974</a>]</span>, Session Initiation Protocol (SIP) <span>[<a href="#RFC3261" class="xref">RFC3261</a>]</span>, Real-Time Streaming Protocol (RTSP) <span>[<a href="#RFC7826" class="xref">RFC7826</a>]</span>, electronic mail <span>[<a href="#RFC5322" class="xref">RFC5322</a>]</span> using the MIME extensions <span>[<a href="#RFC2045" class="xref">RFC2045</a>]</span>,
      and the Hypertext Transport Protocol (HTTP) <span>[<a href="#RFC7230" class="xref">RFC7230</a>]</span>.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">SDP is intended to be general purpose so that it can be used in a
      wide range of network environments and applications. However, it is not
      intended to support negotiation of session content or media encodings:
      this is viewed as outside the scope of session description.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">This memo obsoletes <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span>. The changes relative to
      <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span> are outlined in <a href="#changes" class="xref">Section 10</a> of this memo.<a href="#section-1-4" class="pilcrow">¶</a></p>
</section>
<section id="section-2">
      <h2 id="name-glossary-of-terms">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-glossary-of-terms" class="section-name selfRef">Glossary of Terms</a>
      </h2>
<p id="section-2-1">The following terms are used in this document and have specific meaning
      within the context of this document.<a href="#section-2-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2-2">
        <dt id="section-2-2.1">Session Description:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.2">A well-defined format for
          conveying sufficient information to discover and participate in a
          multimedia session.<a href="#section-2-2.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.3">Media Description:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.4">A Media Description contains the information 
          needed for one party to establish an application-layer network protocol 
          connection to another party. It starts with an "m=" line and is terminated 
          by either the next "m=" line or by the end of the session description.<a href="#section-2-2.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.5">Session-Level Section:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.6">This refers to the parts that are not media descriptions, whereas the session description refers to the whole body that includes the session-level section and the media description(s).<a href="#section-2-2.6" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-2-3">The terms "multimedia conference" and "multimedia session" are used
      in this document as defined in <span>[<a href="#RFC7656" class="xref">RFC7656</a>]</span>. The terms
      "session" and "multimedia session" are used interchangeably in this
      document.<a href="#section-2-3" class="pilcrow">¶</a></p>
<p id="section-2-4">
    The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>", "<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL NOT</span>", "<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>", "<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
    "<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are to be interpreted as
    described in BCP 14 <span>[<a href="#RFC2119" class="xref">RFC2119</a>]</span> <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> 
    when, and only when, they appear in all capitals, as shown here.<a href="#section-2-4" class="pilcrow">¶</a></p>
</section>
<div id="usage_examples">
<section id="section-3">
      <h2 id="name-examples-of-sdp-usage">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-examples-of-sdp-usage" class="section-name selfRef">Examples of SDP Usage</a>
      </h2>
<section id="section-3.1">
        <h3 id="name-session-initiation">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-session-initiation" class="section-name selfRef">Session Initiation</a>
        </h3>
<p id="section-3.1-1">The <span><a href="#RFC3261" class="xref">Session Initiation Protocol (SIP)</a> [<a href="#RFC3261" class="xref">RFC3261</a>]</span>
        is an application-layer control protocol for creating, modifying, and
        terminating sessions such as Internet multimedia conferences, Internet
        telephone calls, and multimedia distribution. The SIP messages used to
        create sessions carry session descriptions that allow participants to
        agree on a set of compatible media types <span>[<a href="#RFC6838" class="xref">RFC6838</a>]</span>. 
        These session descriptions
        are commonly formatted using SDP. When used with SIP, the <span><a href="#RFC3264" class="xref">offer/answer model</a> [<a href="#RFC3264" class="xref">RFC3264</a>]</span> provides a limited
        framework for negotiation using SDP.<a href="#section-3.1-1" class="pilcrow">¶</a></p>
</section>
<section id="section-3.2">
        <h3 id="name-streaming-media">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-streaming-media" class="section-name selfRef">Streaming Media</a>
        </h3>
<p id="section-3.2-1">The <span><a href="#RFC7826" class="xref">Real-Time Streaming Protocol
        (RTSP)</a> [<a href="#RFC7826" class="xref">RFC7826</a>]</span>, is an application-level protocol for control over the
        delivery of data with real-time properties. RTSP provides an
        extensible framework to enable controlled, on-demand delivery of
        real-time data, such as audio and video. An RTSP client and server
        negotiate an appropriate set of parameters for media delivery,
        partially using SDP syntax to describe those parameters.<a href="#section-3.2-1" class="pilcrow">¶</a></p>
</section>
<section id="section-3.3">
        <h3 id="name-email-and-the-world-wide-we">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-email-and-the-world-wide-we" class="section-name selfRef">Email and the World Wide Web</a>
        </h3>
<p id="section-3.3-1">Alternative means of conveying session descriptions include
        electronic mail and the World Wide Web (WWW). For both email and WWW
        distribution, the media type "application/sdp" is used. This enables
        the automatic launching of applications for participation in the
        session from the WWW client or mail reader in a standard manner.<a href="#section-3.3-1" class="pilcrow">¶</a></p>
<p id="section-3.3-2">Note that descriptions of multicast sessions sent only via email
        or the WWW do not have the property that the receiver of a session
        description can necessarily receive the session because the multicast
        sessions may be restricted in scope, and access to the WWW server or
        reception of email is possibly outside this scope.<a href="#section-3.3-2" class="pilcrow">¶</a></p>
</section>
<section id="section-3.4">
        <h3 id="name-multicast-session-announcem">
<a href="#section-3.4" class="section-number selfRef">3.4. </a><a href="#name-multicast-session-announcem" class="section-name selfRef">Multicast Session Announcement</a>
        </h3>
<p id="section-3.4-1">In order to assist the advertisement of multicast multimedia
        conferences and other multicast sessions, and to communicate the
        relevant session setup information to prospective participants, a
        distributed session directory may be used. An instance of such a
        session directory periodically sends packets containing a description
        of the session to a well-known multicast group. These advertisements
        are received by other session directories such that potential remote
        participants can use the session description to start the tools
        required to participate in the session.<a href="#section-3.4-1" class="pilcrow">¶</a></p>
<p id="section-3.4-2">One protocol used to implement such a distributed directory is the
        <span><a href="#RFC2974" class="xref">SAP</a> [<a href="#RFC2974" class="xref">RFC2974</a>]</span>. SDP provides the recommended
        session description format for such session announcements.<a href="#section-3.4-2" class="pilcrow">¶</a></p>
</section>
</section>
</div>
<section id="section-4">
      <h2 id="name-requirements-and-recommenda">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-requirements-and-recommenda" class="section-name selfRef">Requirements and Recommendations</a>
      </h2>
<p id="section-4-1">The purpose of SDP is to convey information about media streams in
      multimedia sessions to allow the recipients of a session description to
      participate in the session. SDP is primarily intended for use with
      Internet protocols, although it is sufficiently general that it can describe
      multimedia conferences in other network environments. Media streams can
      be many-to-many. Sessions need not be continually active.<a href="#section-4-1" class="pilcrow">¶</a></p>
<p id="section-4-2">Thus far, multicast-based sessions on the Internet have differed from
      many other forms of conferencing in that anyone receiving the traffic
      can join the session (unless the session traffic is encrypted). In such
      an environment, SDP serves two primary purposes. It is a means to
      communicate the existence of a session, and it is a means to convey
      sufficient information to enable joining and participating in the
      session. In a unicast environment, only the latter purpose is likely to
      be relevant.<a href="#section-4-2" class="pilcrow">¶</a></p>
<p id="section-4-3">An SDP description includes the following:<a href="#section-4-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4-4.1">Session name and purpose<a href="#section-4-4.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-4-4.2">Time(s) the session is active<a href="#section-4-4.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-4-4.3">The media comprising the session<a href="#section-4-4.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-4-4.4">Information needed to receive those media (addresses, ports,
          formats, etc.)<a href="#section-4-4.4" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-4-5">As resources necessary to participate in a session may be limited,
      some additional information may also be desirable:<a href="#section-4-5" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4-6.1">Information about the bandwidth to be used by the session<a href="#section-4-6.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-4-6.2">Contact information for the person responsible for the
          session<a href="#section-4-6.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-4-7">In general, SDP must convey sufficient information to enable
      applications to join a session (with the possible exception of
      encryption keys) and to announce the resources to be used to any
      nonparticipants that may need to know. (This latter feature is
      primarily useful when SDP is used with a multicast session announcement
      protocol.)<a href="#section-4-7" class="pilcrow">¶</a></p>
<section id="section-4.1">
        <h3 id="name-media-and-transport-informa">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-media-and-transport-informa" class="section-name selfRef">Media and Transport Information</a>
        </h3>
<p id="section-4.1-1">An SDP description includes the following media information:<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.1-2.1">The type of media (video, audio, etc.)<a href="#section-4.1-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.1-2.2">The media transport protocol (RTP/UDP/IP, H.320, etc.)<a href="#section-4.1-2.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.1-2.3">The format of the media (H.261 video, MPEG video, etc.)<a href="#section-4.1-2.3" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.1-3">In addition to media format and transport protocol, SDP conveys
        address and port details. For an IP multicast session, these
        comprise:<a href="#section-4.1-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.1-4.1">The multicast group address for media<a href="#section-4.1-4.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.1-4.2">The transport port for media<a href="#section-4.1-4.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.1-5">This address and port are the destination address and destination
        port of the multicast stream, whether being sent, received, or
        both.<a href="#section-4.1-5" class="pilcrow">¶</a></p>
<p id="section-4.1-6">For unicast IP sessions, the following are conveyed:<a href="#section-4.1-6" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.1-7.1">The remote address for media<a href="#section-4.1-7.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.1-7.2">The remote transport port for media<a href="#section-4.1-7.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.1-8">The semantics of the address and port depend on context. 
        Typically, this <span class="bcp14">SHOULD</span> be the remote address and remote port 
        to which media is to be sent or received. 
        Details may differ based on the network type, address type, 
        protocol, and media specified, and whether the SDP is being distributed 
        as an advertisement or negotiated in an offer/answer <span>[<a href="#RFC3264" class="xref">RFC3264</a>]</span> exchange.
        (E.g., Some address types or protocols may not have a notion of port.) 
        Deviating from typical behavior should be done cautiously 
        since this complicates implementations (including middleboxes that must 
        parse the addresses to open Network Address Translation (NAT) or 
        firewall pinholes).<a href="#section-4.1-8" class="pilcrow">¶</a></p>
</section>
<section id="section-4.2">
        <h3 id="name-timing-information">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-timing-information" class="section-name selfRef">Timing Information</a>
        </h3>
<p id="section-4.2-1">Sessions may be either bounded or unbounded in time. Whether or not
        they are bounded, they may be only active at specific times. SDP can
        convey:<a href="#section-4.2-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.2-2.1">An arbitrary list of start and stop times bounding the
            session<a href="#section-4.2-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-2.2">For each bound, repeat times such as "every Wednesday at 10am
            for one hour"<a href="#section-4.2-2.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.2-3">This timing information is globally consistent, irrespective of
        local time zone or daylight saving time (see <a href="#timing" class="xref">Section 5.9</a>).<a href="#section-4.2-3" class="pilcrow">¶</a></p>
</section>
<section id="section-4.3">
        <h3 id="name-obtaining-further-informati">
<a href="#section-4.3" class="section-number selfRef">4.3. </a><a href="#name-obtaining-further-informati" class="section-name selfRef">Obtaining Further Information about a Session</a>
        </h3>
<p id="section-4.3-1">A session description could convey enough information to decide
        whether or not to participate in a session. SDP may include additional
        pointers in the form of Uniform Resource Identifiers (URIs) <span>[<a href="#RFC3986" class="xref">RFC3986</a>]</span> 
        for more information about the session.
        (Note that use of URIs to indicate remote resources is subject to 
        the security considerations from <span>[<a href="#RFC3986" class="xref">RFC3986</a>]</span>.)<a href="#section-4.3-1" class="pilcrow">¶</a></p>
</section>
<section id="section-4.4">
        <h3 id="name-internationalization">
<a href="#section-4.4" class="section-number selfRef">4.4. </a><a href="#name-internationalization" class="section-name selfRef">Internationalization</a>
        </h3>
<p id="section-4.4-1">The SDP specification recommends the use of the ISO 10646 character
        set in the UTF-8 encoding <span>[<a href="#RFC3629" class="xref">RFC3629</a>]</span> to allow many
        different languages to be represented. However, to assist in compact
        representations, SDP also allows other character sets such as
        <span>[<a href="#ISO.8859-1.1998" class="xref">ISO.8859-1.1998</a>]</span> to be used when desired. 
        Internationalization only applies to
        free-text subfields (session name and background information), and not to
        SDP as a whole.<a href="#section-4.4-1" class="pilcrow">¶</a></p>
</section>
</section>
<div id="SDP-specification">
<section id="section-5">
      <h2 id="name-sdp-specification">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-sdp-specification" class="section-name selfRef">SDP Specification</a>
      </h2>
<p id="section-5-1">An SDP description is denoted by the media type "application/sdp"
      (See <a href="#iana" class="xref">Section 8</a>).<a href="#section-5-1" class="pilcrow">¶</a></p>
<p id="section-5-2">An SDP description is entirely textual. SDP field names and attribute
      names use only the US-ASCII subset of UTF-8 <span>[<a href="#RFC3629" class="xref">RFC3629</a>]</span>, 
      but textual fields and
      attribute values <span class="bcp14">MAY</span> use the full ISO 10646 character set in UTF-8
      encoding, or some other character set defined by the "a=charset:"
      attribute (<a href="#charset" class="xref">Section 6.10</a>). 
      Field and attribute values that use the full UTF-8 character
      set are never directly compared, hence there is no requirement for UTF-8
      normalization. The textual form, as opposed to a binary encoding such as
      ASN.1 or XDR, was chosen to enhance portability, to enable a variety of
      transports to be used, and to allow flexible, text-based toolkits to be
      used to generate and process session descriptions. However, since SDP
      may be used in environments where the maximum permissible size of a
      session description is limited, the encoding is deliberately compact.
      Also, since descriptions may be transported via very unreliable means
      or damaged by an intermediate caching server, the encoding was designed
      with strict order and formatting rules so that most errors would result
      in malformed session descriptions that could be detected easily and
      discarded.<a href="#section-5-2" class="pilcrow">¶</a></p>
<p id="section-5-3">An SDP description consists of a number of lines of text of the
      form:<a href="#section-5-3" class="pilcrow">¶</a></p>
<div id="section-5-4">
<pre class="sourcecode">
   &lt;type&gt;=&lt;value&gt;
</pre><a href="#section-5-4" class="pilcrow">¶</a>
</div>
<p id="section-5-5">where &lt;type&gt; is exactly one case-significant character and
      &lt;value&gt; is structured text whose format depends on &lt;type&gt;.
      In general, &lt;value&gt; is either a number of subfields delimited by a
      single space character or a free format string, and is case-significant
      unless a specific field defines otherwise. Whitespace separators are not used
      on either side of the "=" sign, however, the value can contain a leading
      whitespace as part of its syntax, i.e., that whitespace is part of the value.<a href="#section-5-5" class="pilcrow">¶</a></p>
<p id="section-5-6">An SDP description <span class="bcp14">MUST</span> conform to the syntax defined in <a href="#abnf" class="xref">Section 9</a>.
      The following is an overview of the syntax.<a href="#section-5-6" class="pilcrow">¶</a></p>
<p id="section-5-7">An SDP description consists of a session-level section followed by
      zero or more media descriptions. The session-level section starts with a
      "v=" line and continues to the first media description (or the end of
      the whole description, whichever comes first). Each media description
      starts with an "m=" line and continues to the next media description
      or the end of the whole session description, whichever comes first. In
      general, session-level values are the default for all media unless
      overridden by an equivalent media-level value.<a href="#section-5-7" class="pilcrow">¶</a></p>
<p id="section-5-8">Some lines in each description are required and some are optional,
      but when present, they must appear in exactly the order given here. (The fixed order
      greatly enhances error detection and allows for a simple parser).
      In the following overview, optional items are marked with a "*".<a href="#section-5-8" class="pilcrow">¶</a></p>
<div id="section-5-9">
<pre class="sourcecode">
   Session description
      v=  (protocol version)
      o=  (originator and session identifier)
      s=  (session name)
      i=* (session information)
      u=* (URI of description)
      e=* (email address)
      p=* (phone number)
      c=* (connection information -- not required if included in
           all media descriptions)
      b=* (zero or more bandwidth information lines)
      One or more time descriptions:
        ("t=", "r=" and "z=" lines; see below)
      k=* (obsolete)
      a=* (zero or more session attribute lines)
      Zero or more media descriptions

   Time description
      t=  (time the session is active)
      r=* (zero or more repeat times)
      z=* (optional time zone offset line)

   Media description, if present
      m=  (media name and transport address)
      i=* (media title)
      c=* (connection information -- optional if included at
           session level)
      b=* (zero or more bandwidth information lines)
      k=* (obsolete)
      a=* (zero or more media attribute lines)
</pre><a href="#section-5-9" class="pilcrow">¶</a>
</div>
<p id="section-5-10">The set of type letters is deliberately small and not intended to be
      extensible -- an SDP parser <span class="bcp14">MUST</span> completely ignore or reject any session
      description that contains a type letter that it does not understand. The
      attribute mechanism ("a=", described in <a href="#attribspec" class="xref">Section 5.13</a>) is the primary means for
      extending SDP and tailoring it to particular applications or media. Some
      attributes (the ones listed in <a href="#attrs" class="xref">Section 6</a>) have
      a defined meaning, but others may be added on a media-
      or session-specific basis. (Attribute scopes in addition to media-specific
      and session-specific scopes may also be defined in extensions to this document,
      e.g., <span>[<a href="#RFC5576" class="xref">RFC5576</a>]</span> and <span>[<a href="#RFC8864" class="xref">RFC8864</a>]</span>.)
      An SDP parser <span class="bcp14">MUST</span> ignore any attribute it doesn't understand.<a href="#section-5-10" class="pilcrow">¶</a></p>
<p id="section-5-11">An SDP description may contain URIs that reference external content
      in the "u=", "k=", and "a=" lines. These URIs may be dereferenced in
      some cases, making the session description non-self-contained.<a href="#section-5-11" class="pilcrow">¶</a></p>
<p id="section-5-12">The connection ("c=") information in the session-level section
      applies to all the media descriptions of that session unless overridden by connection
      information in the media description. 
      For instance, in the example below, each audio media description behaves as if 
      it were given a "c=IN IP4 198.51.100.1".<a href="#section-5-12" class="pilcrow">¶</a></p>
<p id="section-5-13">An example SDP description is:<a href="#section-5-13" class="pilcrow">¶</a></p>
<div id="section-5-14">
<pre class="sourcecode lang-sdp">
      v=0
      o=jdoe 3724394400 3724394405 IN IP4 198.51.100.1
      s=Call to John Smith
      i=SDP Offer #1
      u=http://www.jdoe.example.com/home.html
      e=Jane Doe &lt;jane@jdoe.example.com&gt;
      p=+1 617 555-6011
      c=IN IP4 198.51.100.1
      t=0 0
      m=audio 49170 RTP/AVP 0
      m=audio 49180 RTP/AVP 0
      m=video 51372 RTP/AVP 99
      c=IN IP6 2001:db8::2
      a=rtpmap:99 h263-1998/90000
</pre><a href="#section-5-14" class="pilcrow">¶</a>
</div>
<p id="section-5-15">Text-containing fields such as the session-name-field and information-field are octet
      strings that may contain any octet with the exceptions of 0x00 (Nul),
      0x0a (ASCII newline), and 0x0d (ASCII carriage return). The sequence
      CRLF (0x0d0a) is used to end a line, although parsers <span class="bcp14">SHOULD</span> be
      tolerant and also accept lines terminated with a single newline
      character. If the "a=charset:" attribute is not present, these octet
      strings <span class="bcp14">MUST</span> be interpreted as containing ISO-10646 characters in UTF-8
      encoding. When the "a=charset:" attribute is present the session-name-field,
      information-field, and some attribute fields are interpreted according
      to the selected character set.<a href="#section-5-15" class="pilcrow">¶</a></p>
<p id="section-5-16">A session description can contain domain names in the "o=", "u=",
      "e=", "c=", and "a=" lines. Any domain name used in SDP <span class="bcp14">MUST</span> comply with
      <span>[<a href="#RFC1034" class="xref">RFC1034</a>]</span> and <span>[<a href="#RFC1035" class="xref">RFC1035</a>]</span>. Internationalized
      domain names (IDNs) <span class="bcp14">MUST</span> be represented using the ASCII Compatible
      Encoding (ACE) form defined in <span>[<a href="#RFC5890" class="xref">RFC5890</a>]</span> and <span class="bcp14">MUST NOT</span> be
      directly represented in UTF-8 or any other encoding (this requirement is
      for compatibility with <span>[<a href="#RFC2327" class="xref">RFC2327</a>]</span> and other early
      SDP-related standards, which predate the development of
      internationalized domain names).<a href="#section-5-16" class="pilcrow">¶</a></p>
<section id="section-5.1">
        <h3 id="name-protocol-version-v">
<a href="#section-5.1" class="section-number selfRef">5.1. </a><a href="#name-protocol-version-v" class="section-name selfRef">Protocol Version ("v=")</a>
        </h3>
<div id="section-5.1-1">
<pre class="sourcecode lang-sdp">
      v=0
</pre><a href="#section-5.1-1" class="pilcrow">¶</a>
</div>
<p id="section-5.1-2">The "v=" line (version-field) gives the version of the Session Description
        Protocol. This memo defines version 0. There is no minor version
        number.<a href="#section-5.1-2" class="pilcrow">¶</a></p>
</section>
<div id="origin">
<section id="section-5.2">
        <h3 id="name-origin-o">
<a href="#section-5.2" class="section-number selfRef">5.2. </a><a href="#name-origin-o" class="section-name selfRef">Origin ("o=")</a>
        </h3>
<div id="section-5.2-1">
<pre class="sourcecode">
     o=&lt;username&gt; &lt;sess-id&gt; &lt;sess-version&gt; &lt;nettype&gt; &lt;addrtype&gt;
     &lt;unicast-address&gt;
</pre><a href="#section-5.2-1" class="pilcrow">¶</a>
</div>
<p id="section-5.2-2">The "o=" line (origin-field) gives the originator of the session (her username and
        the address of the user's host) plus a session identifier and version
        number:<a href="#section-5.2-2" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-5.2-3">
          <dt id="section-5.2-3.1">&lt;username&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.2-3.2">is the user's login on the
            originating host, or it is "-" if the originating host does not
            support the concept of user IDs. The &lt;username&gt; <span class="bcp14">MUST NOT</span>
            contain spaces.<a href="#section-5.2-3.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.2-3.3">&lt;sess-id&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.2-3.4">is a numeric string such that the
            tuple of &lt;username&gt;, &lt;sess-id&gt;, &lt;nettype&gt;,
            &lt;addrtype&gt;, and &lt;unicast-address&gt; forms a globally
            unique identifier for the session. The method of &lt;sess-id&gt;
            allocation is up to the creating tool, but a timestamp, 
            in seconds since January 1, 1900 UTC, is recommended 
            to ensure uniqueness.<a href="#section-5.2-3.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.2-3.5">&lt;sess-version&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.2-3.6">is a version number for this
            session description. Its usage is up to the creating tool, so long
            as &lt;sess-version&gt; is increased when a modification is made
            to the session description. Again, as with &lt;sess-id&gt; 
            it is <span class="bcp14">RECOMMENDED</span> that a timestamp be used.<a href="#section-5.2-3.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.2-3.7">&lt;nettype&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.2-3.8">is a text string giving the type of
            network. Initially, "IN" is defined to have the meaning "Internet",
            but other values <span class="bcp14">MAY</span> be registered in the future (see <a href="#iana" class="xref">Section 8</a>).<a href="#section-5.2-3.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.2-3.9">&lt;addrtype&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.2-3.10">is a text string giving the type of
            the address that follows. Initially, "IP4" and "IP6" are defined,
            but other values <span class="bcp14">MAY</span> be registered in the future (see <a href="#iana" class="xref">Section 8</a>).<a href="#section-5.2-3.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.2-3.11">&lt;unicast-address&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.2-3.12">is an address of the machine
            from which the session was created. For an address type of "IP4",
            this is either a fully qualified domain name of the machine or the
            dotted-decimal representation of an IP version 4 address of the
            machine. For an address type of "IP6", this is either a fully
            qualified domain name of the machine or the address of the machine 
            represented as specified in <span><a href="https://www.rfc-editor.org/rfc/rfc5952#section-4" class="relref">Section 4</a> of [<a href="#RFC5952" class="xref">RFC5952</a>]</span>.
            For both "IP4" and "IP6", the fully qualified domain name is the form that
            <span class="bcp14">SHOULD</span> be given unless this is unavailable, in which case a
            globally unique address <span class="bcp14">MAY</span> be substituted.<a href="#section-5.2-3.12" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-5.2-4">In general, the "o=" line serves as a globally unique identifier
        for this version of the session description, and the subfields
        excepting the version, taken together identify the session irrespective
        of any modifications.<a href="#section-5.2-4" class="pilcrow">¶</a></p>
<p id="section-5.2-5">For privacy reasons, it is sometimes desirable to obfuscate the
        username and IP address of the session originator. If this is a
        concern, an arbitrary &lt;username&gt; and private
        &lt;unicast-address&gt; <span class="bcp14">MAY</span> be chosen to populate the "o=" line,
        provided that these are selected in a manner that does not affect the
        global uniqueness of the field.<a href="#section-5.2-5" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-5.3">
        <h3 id="name-session-name-s">
<a href="#section-5.3" class="section-number selfRef">5.3. </a><a href="#name-session-name-s" class="section-name selfRef">Session Name ("s=")</a>
        </h3>
<div id="section-5.3-1">
<pre class="sourcecode">
   s=&lt;session name&gt;
</pre><a href="#section-5.3-1" class="pilcrow">¶</a>
</div>
<p id="section-5.3-2">The "s=" line (session-name-field) is the textual session name. 
        There <span class="bcp14">MUST</span> be one and only one "s=" line per session description. 
        The "s=" line <span class="bcp14">MUST NOT</span> be empty. If a session has no meaningful name, 
        then "s= " or "s=-" (i.e., a single space or dash as the session name) is <span class="bcp14">RECOMMENDED</span>.
        If a session-level "a=charset:" attribute is present, it specifies the character set used 
        in the "s=" field. If a session-level "a=charset:" attribute is not present, 
        the "s=" field <span class="bcp14">MUST</span> contain ISO 10646 characters in UTF-8 encoding.<a href="#section-5.3-2" class="pilcrow">¶</a></p>
</section>
<section id="section-5.4">
        <h3 id="name-session-information-i">
<a href="#section-5.4" class="section-number selfRef">5.4. </a><a href="#name-session-information-i" class="section-name selfRef">Session Information ("i=")</a>
        </h3>
<div id="section-5.4-1">
<pre class="sourcecode">
   i=&lt;session information&gt;
</pre><a href="#section-5.4-1" class="pilcrow">¶</a>
</div>
<p id="section-5.4-2">The "i=" line (information-field) provides textual information about the session. There
        can be at most one session-level "i=" line per session description,
        and at most one "i=" line in each media description. Unless a
        media-level "i=" line is provided, the session-level "i=" line applies
        to that media description. If the "a=charset:" attribute is present, it
        specifies the character set used in the "i=" line. If the "a=charset:"
        attribute is not present, the "i=" line <span class="bcp14">MUST</span> contain ISO 10646
        characters in UTF-8 encoding.<a href="#section-5.4-2" class="pilcrow">¶</a></p>
<p id="section-5.4-3">At most one "i=" line can be used for each media description. In media
        definitions, "i=" lines are primarily intended for labeling media
        streams. As such, they are most likely to be useful when a single
        session has more than one distinct media stream of the same media
        type. An example would be two different whiteboards, one for slides
        and one for feedback and questions.<a href="#section-5.4-3" class="pilcrow">¶</a></p>
<p id="section-5.4-4">The "i=" line is intended to provide a free-form human-readable
        description of the session or the purpose of a media stream. It is not
        suitable for parsing by automata.<a href="#section-5.4-4" class="pilcrow">¶</a></p>
</section>
<section id="section-5.5">
        <h3 id="name-uri-u">
<a href="#section-5.5" class="section-number selfRef">5.5. </a><a href="#name-uri-u" class="section-name selfRef">URI ("u=")</a>
        </h3>
<div id="section-5.5-1">
<pre class="sourcecode">
   u=&lt;uri&gt;
</pre><a href="#section-5.5-1" class="pilcrow">¶</a>
</div>
<p id="section-5.5-2">The "u=" line (uri-field) provides a URI (Uniform Resource Identifier) 
        <span>[<a href="#RFC3986" class="xref">RFC3986</a>]</span>. The URI should be a pointer to additional
        human readable information about the session. 
        This line is <span class="bcp14">OPTIONAL</span>. No more than one
        "u=" line is allowed per session description.<a href="#section-5.5-2" class="pilcrow">¶</a></p>
</section>
<section id="section-5.6">
        <h3 id="name-email-address-and-phone-num">
<a href="#section-5.6" class="section-number selfRef">5.6. </a><a href="#name-email-address-and-phone-num" class="section-name selfRef">Email Address and Phone Number ("e=" and "p=")</a>
        </h3>
<div id="section-5.6-1">
<pre class="sourcecode">
   e=&lt;email-address&gt;
   p=&lt;phone-number&gt;
</pre><a href="#section-5.6-1" class="pilcrow">¶</a>
</div>
<p id="section-5.6-2">The "e=" line (email-field) and "p=" line (phone-field) specify contact information for the person
        responsible for the session. This is not necessarily the same person
        that created the session description.<a href="#section-5.6-2" class="pilcrow">¶</a></p>
<p id="section-5.6-3">Inclusion of an email address or phone number is <span class="bcp14">OPTIONAL</span>.<a href="#section-5.6-3" class="pilcrow">¶</a></p>
<p id="section-5.6-4">If an email address or phone number is present, it <span class="bcp14">MUST</span> be
        specified before the first media description. More than one email or phone
        line can be given for a session description.<a href="#section-5.6-4" class="pilcrow">¶</a></p>
<p id="section-5.6-5">Phone numbers <span class="bcp14">SHOULD</span> be given in the form of an international
        public telecommunication number (see ITU-T Recommendation E.164 <span>[<a href="#E164" class="xref">E164</a>]</span>)
        preceded by a "+". Spaces and hyphens may be used to split up a phone-field
        to aid readability if desired. For example:<a href="#section-5.6-5" class="pilcrow">¶</a></p>
<div id="section-5.6-6">
<pre class="sourcecode lang-sdp">
   p=+1 617 555-6011
</pre><a href="#section-5.6-6" class="pilcrow">¶</a>
</div>
<p id="section-5.6-7">Both email addresses and phone numbers can have an <span class="bcp14">OPTIONAL</span> free
        text string associated with them, normally giving the name of the
        person who may be contacted. This <span class="bcp14">MUST</span> be enclosed in parentheses if
        it is present. For example:<a href="#section-5.6-7" class="pilcrow">¶</a></p>
<div id="section-5.6-8">
<pre class="sourcecode lang-sdp">
   e=j.doe@example.com (Jane Doe)
</pre><a href="#section-5.6-8" class="pilcrow">¶</a>
</div>
<p id="section-5.6-9">The alternative <span>[<a href="#RFC5322" class="xref">RFC5322</a>]</span> name quoting convention is
        also allowed for both email addresses and phone numbers. For
        example:<a href="#section-5.6-9" class="pilcrow">¶</a></p>
<div id="section-5.6-10">
<pre class="sourcecode lang-sdp">
   e=Jane Doe &lt;j.doe@example.com&gt;
</pre><a href="#section-5.6-10" class="pilcrow">¶</a>
</div>
<p id="section-5.6-11">The free text string <span class="bcp14">SHOULD</span> be in the ISO-10646 character set with
        UTF-8 encoding, or alternatively in ISO-8859-1 or other encodings if
        the appropriate session-level "a=charset:" attribute is set.<a href="#section-5.6-11" class="pilcrow">¶</a></p>
</section>
<div id="connection-information">
<section id="section-5.7">
        <h3 id="name-connection-information-c">
<a href="#section-5.7" class="section-number selfRef">5.7. </a><a href="#name-connection-information-c" class="section-name selfRef">Connection Information ("c=")</a>
        </h3>
<div id="section-5.7-1">
<pre class="sourcecode">
   c=&lt;nettype&gt; &lt;addrtype&gt; &lt;connection-address&gt;
</pre><a href="#section-5.7-1" class="pilcrow">¶</a>
</div>
<p id="section-5.7-2">The "c=" line (connection-field) contains information necessary
        to establish a network connection.<a href="#section-5.7-2" class="pilcrow">¶</a></p>
<p id="section-5.7-3">A session description <span class="bcp14">MUST</span> contain either at least one "c=" line in
        each media description or a single "c=" line at the session level. It
        <span class="bcp14">MAY</span> contain a single session-level "c=" line and additional media-level "c="
        line(s) per-media-description, in which case the media-level values
        override the session-level settings for the respective media.<a href="#section-5.7-3" class="pilcrow">¶</a></p>
<p id="section-5.7-4">The first subfield (&lt;nettype&gt;) is the network type, which
        is a text string giving the type of network. Initially, "IN" is
        defined to have the meaning "Internet", but other values <span class="bcp14">MAY</span> be
        registered in the future (see <a href="#iana" class="xref">Section 8</a>).<a href="#section-5.7-4" class="pilcrow">¶</a></p>
<p id="section-5.7-5">The second subfield (&lt;addrtype&gt;) is the address type. This
        allows SDP to be used for sessions that are not IP based. This memo
        only defines "IP4" and "IP6", but other values <span class="bcp14">MAY</span> be registered in the
        future (see <a href="#iana" class="xref">Section 8</a>).<a href="#section-5.7-5" class="pilcrow">¶</a></p>
<p id="section-5.7-6">The third subfield (&lt;connection-address&gt;) is the
        connection address. Additional subfields <span class="bcp14">MAY</span> be added after the
        connection address depending on the value of the &lt;addrtype&gt;
        subfield.<a href="#section-5.7-6" class="pilcrow">¶</a></p>
<p id="section-5.7-7">When the &lt;addrtype&gt; is "IP4" or "IP6", the connection address is
        defined as follows:<a href="#section-5.7-7" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-5.7-8.1">If the session is multicast, the connection address will be an
            IP multicast group address. If the session is not multicast, then
            the connection address contains the unicast IP address of the
            expected data source, data relay, or data sink as determined by
            additional attribute-fields (<a href="#attribspec" class="xref">Section 5.13</a>). 
            It is not expected that unicast
            addresses will be given in a session description that is
            communicated by a multicast announcement, though this is not
            prohibited.<a href="#section-5.7-8.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-5.7-8.2">Sessions using an "IP4" multicast connection address <span class="bcp14">MUST</span> also
            have a time to live (TTL) value present in addition to the
            multicast address. The TTL and the address together define the
            scope with which multicast packets sent in this session will be
            sent. TTL values <span class="bcp14">MUST</span> be in the range 0-255. Although the TTL <span class="bcp14">MUST</span>
            be specified, its use to scope multicast traffic is deprecated;
            applications <span class="bcp14">SHOULD</span> use an administratively scoped address
            instead.<a href="#section-5.7-8.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-5.7-9">The TTL for the session is appended to the address using a slash as
        a separator. An example is:<a href="#section-5.7-9" class="pilcrow">¶</a></p>
<div id="section-5.7-10">
<pre class="sourcecode lang-sdp">
   c=IN IP4 233.252.0.1/127
</pre><a href="#section-5.7-10" class="pilcrow">¶</a>
</div>
<p id="section-5.7-11">"IP6" multicast does not use TTL scoping, and hence the TTL value
        <span class="bcp14">MUST NOT</span> be present for "IP6" multicast. It is expected that IPv6 scoped
        addresses will be used to limit the scope of multimedia
        conferences.<a href="#section-5.7-11" class="pilcrow">¶</a></p>
<p id="section-5.7-12">Hierarchical or layered encoding schemes are data streams where the
        encoding from a single media source is split into a number of layers.
        The receiver can choose the desired quality (and hence bandwidth) by
        only subscribing to a subset of these layers. Such layered encodings
        are normally transmitted in multiple multicast groups to allow
        multicast pruning. This technique keeps unwanted traffic from sites
        only requiring certain levels of the hierarchy. For applications
        requiring multiple multicast groups, we allow the following notation
        to be used for the connection address:<a href="#section-5.7-12" class="pilcrow">¶</a></p>
<div id="section-5.7-13">
<pre class="sourcecode">
   &lt;base multicast address&gt;[/&lt;ttl&gt;]/&lt;number of addresses&gt;
</pre><a href="#section-5.7-13" class="pilcrow">¶</a>
</div>
<p id="section-5.7-14">If the number of addresses is not given, it is assumed to be one.
        Multicast addresses so assigned are contiguously allocated above the
        base address, so that, for example:<a href="#section-5.7-14" class="pilcrow">¶</a></p>
<div id="section-5.7-15">
<pre class="sourcecode lang-sdp">
   c=IN IP4 233.252.0.1/127/3
</pre><a href="#section-5.7-15" class="pilcrow">¶</a>
</div>
<p id="section-5.7-16">would state that addresses 233.252.0.1, 233.252.0.2, and
        233.252.0.3 are to be used with a TTL of 127. This is semantically
        identical to including multiple "c=" lines in a media description:<a href="#section-5.7-16" class="pilcrow">¶</a></p>
<div id="section-5.7-17">
<pre class="sourcecode lang-sdp">
   c=IN IP4 233.252.0.1/127
   c=IN IP4 233.252.0.2/127
   c=IN IP4 233.252.0.3/127
</pre><a href="#section-5.7-17" class="pilcrow">¶</a>
</div>
<p id="section-5.7-18">Similarly, an IPv6 example would be:<a href="#section-5.7-18" class="pilcrow">¶</a></p>
<div id="section-5.7-19">
<pre class="sourcecode lang-sdp">
   c=IN IP6 ff00::db8:0:101/3
</pre><a href="#section-5.7-19" class="pilcrow">¶</a>
</div>
<p id="section-5.7-20">which is semantically equivalent to:<a href="#section-5.7-20" class="pilcrow">¶</a></p>
<div id="section-5.7-21">
<pre class="sourcecode lang-sdp">
   c=IN IP6 ff00::db8:0:101
   c=IN IP6 ff00::db8:0:102
   c=IN IP6 ff00::db8:0:103
</pre><a href="#section-5.7-21" class="pilcrow">¶</a>
</div>
<p id="section-5.7-22">(remember that the TTL subfield is not present in "IP6"
        multicast).<a href="#section-5.7-22" class="pilcrow">¶</a></p>
<p id="section-5.7-23">Multiple addresses or "c=" lines <span class="bcp14">MAY</span> be specified on a per media description
        basis only if they provide multicast addresses for different layers in
        a hierarchical or layered encoding scheme. Multiple addresses or "c=" lines 
        <span class="bcp14">MUST NOT</span> be specified at session level.<a href="#section-5.7-23" class="pilcrow">¶</a></p>
<p id="section-5.7-24">The slash notation for multiple addresses described above <span class="bcp14">MUST NOT</span>
        be used for IP unicast addresses.<a href="#section-5.7-24" class="pilcrow">¶</a></p>
</section>
</div>
<div id="bandwidthInfo">
<section id="section-5.8">
        <h3 id="name-bandwidth-information-b">
<a href="#section-5.8" class="section-number selfRef">5.8. </a><a href="#name-bandwidth-information-b" class="section-name selfRef">Bandwidth Information ("b=")</a>
        </h3>
<div id="section-5.8-1">
<pre class="sourcecode">
   b=&lt;bwtype&gt;:&lt;bandwidth&gt;
</pre><a href="#section-5.8-1" class="pilcrow">¶</a>
</div>
<p id="section-5.8-2">The <span class="bcp14">OPTIONAL</span> "b=" line (bandwidth-field) denotes the proposed bandwidth to be used by the
        session or media description. The &lt;bwtype&gt; is an alphanumeric modifier
        that provides the meaning of the &lt;bandwidth&gt; number. Two values are
        defined in this specification, but other values <span class="bcp14">MAY</span> be registered in
        the future (see <a href="#iana" class="xref">Section 8</a> and <span>[<a href="#RFC3556" class="xref">RFC3556</a>]</span>,
        <span>[<a href="#RFC3890" class="xref">RFC3890</a>]</span>):<a href="#section-5.8-2" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-5.8-3">
          <dt id="section-5.8-3.1">CT</dt>
          <dd style="margin-left: 1.5em" id="section-5.8-3.2">
            <p id="section-5.8-3.2.1">If the bandwidth of a session is different from
            the bandwidth implicit from the scope, a "b=CT:" line <span class="bcp14">SHOULD</span> be
            supplied for the session giving the proposed upper limit to the
            bandwidth used (the "conference total" bandwidth). Similarly, if
            the bandwidth of bundled media streams 
            <span>[<a href="#RFC8843" class="xref">RFC8843</a>]</span> 
            in an "m=" line is different
            from the implicit value from the scope, a "b=CT:" line <span class="bcp14">SHOULD</span>
            be supplied in the media level. The primary purpose of this is to
            give an approximate idea as to whether two or more sessions (or
            bundled media streams) can coexist simultaneously. Note that a "b=CT:" line
            gives a total bandwidth figure for all the media at all
            endpoints.<a href="#section-5.8-3.2.1" class="pilcrow">¶</a></p>
<p id="section-5.8-3.2.2">The Mux Category for "b=CT:" is NORMAL. This is discussed
            in <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>.<a href="#section-5.8-3.2.2" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-5.8-3.3">AS</dt>
          <dd style="margin-left: 1.5em" id="section-5.8-3.4">
            <p id="section-5.8-3.4.1">The bandwidth is interpreted to be application
            specific (it will be the application's concept of maximum
            bandwidth). Normally, this will coincide with what is set on the
            application's "maximum bandwidth" control if applicable. For
            RTP-based applications, the "b=AS:" line gives the RTP "session bandwidth" as
            defined in <span><a href="https://www.rfc-editor.org/rfc/rfc3550#section-6.2" class="relref">Section 6.2</a> of [<a href="#RFC3550" class="xref">RFC3550</a>]</span>. Note that a "b=AS:" line
            gives a bandwidth figure for a single media at a single endpoint,
            although there may be many endpoints sending simultaneously.<a href="#section-5.8-3.4.1" class="pilcrow">¶</a></p>
<p id="section-5.8-3.4.2">The Mux Category for "b=AS:" is SUM. This is discussed
            in <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>.<a href="#section-5.8-3.4.2" class="pilcrow">¶</a></p>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-5.8-4"><span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span> defined an "X-" prefix for &lt;bwtype&gt; names. 
 This was intended for experimental purposes only. For example:<a href="#section-5.8-4" class="pilcrow">¶</a></p>
<div id="section-5.8-5">
<pre class="sourcecode lang-sdp">
   b=X-YZ:128
</pre><a href="#section-5.8-5" class="pilcrow">¶</a>
</div>
<p id="section-5.8-6">Use of the "X-" prefix is <span class="bcp14">NOT RECOMMENDED</span>. Instead new (non "X-" prefix) &lt;bwtype&gt; names
        <span class="bcp14">SHOULD</span> be defined, and then <span class="bcp14">MUST</span> be registered with IANA in the standard namespace. SDP parsers
        <span class="bcp14">MUST</span> ignore bandwidth-fields with unknown &lt;bwtype&gt; names. The &lt;bwtype&gt; names <span class="bcp14">MUST</span> be
        alphanumeric and, although no length limit is given, it is recommended
        that they be short.<a href="#section-5.8-6" class="pilcrow">¶</a></p>
<p id="section-5.8-7">The &lt;bandwidth&gt; is interpreted as kilobits per second by
        default (including the transport and network-layer, but not the link-layer, overhead). The definition of a new &lt;bwtype&gt; modifier <span class="bcp14">MAY</span> specify
        that the bandwidth is to be interpreted in some alternative unit (the
        "CT" and "AS" modifiers defined in this memo use the default
        units).<a href="#section-5.8-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="timing">
<section id="section-5.9">
        <h3 id="name-time-active-t">
<a href="#section-5.9" class="section-number selfRef">5.9. </a><a href="#name-time-active-t" class="section-name selfRef">Time Active ("t=")</a>
        </h3>
<div id="section-5.9-1">
<pre class="sourcecode">
   t=&lt;start-time&gt; &lt;stop-time&gt;
</pre><a href="#section-5.9-1" class="pilcrow">¶</a>
</div>
<p id="section-5.9-2">A "t=" line (time-field) begins a time description that specifies the start and stop times for a session.
        Multiple time descriptions <span class="bcp14">MAY</span> be used if a session is active at multiple
        irregularly spaced times; each additional time description specifies
        additional periods of time for which the session will be active. If the
        session is active at regular repeat times, a repeat description, 
        begun by an "r=" line (see <a href="#repeattime" class="xref">Section 5.10</a>) can be
        included following the time-field -- in which case the
        time-field specifies the start and stop times of the entire repeat
        sequence.<a href="#section-5.9-2" class="pilcrow">¶</a></p>
<p id="section-5.9-3">The following example specifies two active intervals:<a href="#section-5.9-3" class="pilcrow">¶</a></p>
<div id="section-5.9-4">
<pre class="sourcecode lang-sdp">
   t=3724394400 3724398000 ; Mon 8-Jan-2018 10:00-11:00 UTC
   t=3724484400 3724488000 ; Tue 9-Jan-2018 11:00-12:00 UTC
</pre><a href="#section-5.9-4" class="pilcrow">¶</a>
</div>
<p id="section-5.9-5">The first and second subfields of the time-field give the start and stop times,
        respectively, for the session. These are the decimal
        representation of time values in seconds
        since January 1, 1900 UTC. To convert these values to Unix
        time (UTC), subtract decimal 2208988800.<a href="#section-5.9-5" class="pilcrow">¶</a></p>
<p id="section-5.9-6">Some time representations will
        wrap in the year 2036. Because SDP uses an arbitrary length
        decimal representation, it does not have this issue. Implementations
        of SDP need to be prepared to handle these larger values.<a href="#section-5.9-6" class="pilcrow">¶</a></p>
<p id="section-5.9-7">If the &lt;stop-time&gt; is set to zero, then the session is not
        bounded, though it will not become active until after the
        &lt;start-time&gt;. If the &lt;start-time&gt; is also zero, the
        session is regarded as permanent.<a href="#section-5.9-7" class="pilcrow">¶</a></p>
<p id="section-5.9-8">User interfaces <span class="bcp14">SHOULD</span> strongly discourage the creation of
        unbounded and permanent sessions as they give no information about
        when the session is actually going to terminate, and so make
        scheduling difficult.<a href="#section-5.9-8" class="pilcrow">¶</a></p>
<p id="section-5.9-9">The general assumption may be made, when displaying unbounded
        sessions that have not timed out to the user, that an unbounded
        session will only be active until half an hour from the current time
        or the session start time, whichever is the later. If behavior other
        than this is required, a &lt;stop-time&gt; <span class="bcp14">SHOULD</span> be given and modified as
        appropriate when new information becomes available about when the
        session should really end.<a href="#section-5.9-9" class="pilcrow">¶</a></p>
<p id="section-5.9-10">Permanent sessions may be shown to the user as never being active
        unless there are associated repeat times that state precisely when the
        session will be active.<a href="#section-5.9-10" class="pilcrow">¶</a></p>
</section>
</div>
<div id="repeattime">
<section id="section-5.10">
        <h3 id="name-repeat-times-r">
<a href="#section-5.10" class="section-number selfRef">5.10. </a><a href="#name-repeat-times-r" class="section-name selfRef">Repeat Times ("r=")</a>
        </h3>
<div id="section-5.10-1">
<pre class="sourcecode">
   r=&lt;repeat interval&gt; &lt;active duration&gt; &lt;offsets from start-time&gt;
</pre><a href="#section-5.10-1" class="pilcrow">¶</a>
</div>
<p id="section-5.10-2">An"r=" line (repeat-field) specifies repeat times for a session. 
        If needed to express complex schedules, multiple repeat-fields may
        be included. For example, if a
        session is active at 10am on Monday and 11am on Tuesday for one hour
        each week for three months, then the &lt;start-time&gt; in the
        corresponding "t=" line would be the representation of 10am on the
        first Monday, the &lt;repeat interval&gt; would be 1 week, the
        &lt;active duration&gt; would be 1 hour, and the offsets would be zero
        and 25 hours. The corresponding "t=" line stop time would be the
        representation of the end of the last session three months later. By
        default, all subfields are in seconds, so the "r=" and "t=" lines might
        be the following:<a href="#section-5.10-2" class="pilcrow">¶</a></p>
<div id="section-5.10-3">
<pre class="sourcecode lang-sdp">
   t=3724394400 3730536000 ; Mon 8-Jan-2018 10:00-11:00 UTC
                           ; Tues 20-Mar-2018 12:00 UTC
   r=604800 3600 0 90000   ; 1 week, 1 hour, zero, 25 hours
</pre><a href="#section-5.10-3" class="pilcrow">¶</a>
</div>
<p id="section-5.10-4">To make the description more compact, times may also be given in
        units of days, hours, or minutes. The syntax for these is a number
        immediately followed by a single case-sensitive character. Fractional
        units are not allowed -- a smaller unit should be used instead. The
        following unit specification characters are allowed:<a href="#section-5.10-4" class="pilcrow">¶</a></p>
<span id="name-time-unit-specification-cha"></span><table class="center" id="table-1">
          <caption>
<a href="#table-1" class="selfRef">Table 1</a>:
<a href="#name-time-unit-specification-cha" class="selfRef">Time Unit Specification Characters</a>
          </caption>
<tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">d</td>
              <td class="text-left" rowspan="1" colspan="1">days (86400 seconds)</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">h</td>
              <td class="text-left" rowspan="1" colspan="1">hours (3600 seconds)</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">m</td>
              <td class="text-left" rowspan="1" colspan="1">minutes (60 seconds)</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">s</td>
              <td class="text-left" rowspan="1" colspan="1">seconds (allowed for completeness)</td>
            </tr>
          </tbody>
        </table>
<p id="section-5.10-6">Thus, the above repeat-field could also have been
        written:<a href="#section-5.10-6" class="pilcrow">¶</a></p>
<div id="section-5.10-7">
<pre class="sourcecode lang-sdp">
   r=7d 1h 0 25h
</pre><a href="#section-5.10-7" class="pilcrow">¶</a>
</div>
<p id="section-5.10-8">Monthly and yearly repeats cannot be directly specified with a
        single SDP repeat time; instead, separate time-descriptions should be used to
        explicitly list the session times.<a href="#section-5.10-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="tzadj">
<section id="section-5.11">
        <h3 id="name-time-zone-adjustment-z">
<a href="#section-5.11" class="section-number selfRef">5.11. </a><a href="#name-time-zone-adjustment-z" class="section-name selfRef">Time Zone Adjustment ("z=")</a>
        </h3>
<div id="section-5.11-1">
<pre class="sourcecode">
   z=&lt;adjustment time&gt; &lt;offset&gt; &lt;adjustment time&gt; &lt;offset&gt; ....
</pre><a href="#section-5.11-1" class="pilcrow">¶</a>
</div>
<p id="section-5.11-2">A "z=" line (zone-field) is an optional modifier to the repeat-fields it immediately follows.
        It does not apply to any other fields.<a href="#section-5.11-2" class="pilcrow">¶</a></p>
<p id="section-5.11-3">To schedule a repeated session that spans a change from daylight
        saving time to standard time or vice versa, it is necessary to specify
        offsets from the base time. This is required because different time
        zones change time at different times of day, different countries
        change to or from daylight saving time on different dates, and some
        countries do not have daylight saving time at all.<a href="#section-5.11-3" class="pilcrow">¶</a></p>
<p id="section-5.11-4">Thus, in order to schedule a session that is at the same time
        winter and summer, it must be possible to specify unambiguously by
        whose time zone a session is scheduled. To simplify this task for
        receivers, we allow the sender to specify the time (represented as seconds 
        since January 1, 1900 UTC) that a time zone adjustment happens  
        and the offset from the time when the session
        was first scheduled. The "z=" line allows the sender to specify a list
        of these adjustment times and offsets from the base time.<a href="#section-5.11-4" class="pilcrow">¶</a></p>
<p id="section-5.11-5">An example might be the following:<a href="#section-5.11-5" class="pilcrow">¶</a></p>
<div id="section-5.11-6">
<pre class="sourcecode lang-sdp">
   t=3724394400 3754123200       ; Mon 8-Jan-2018 10:00 UTC
                                 ; Tues 18-Dec-2018 12:00 UTC
   r=604800 3600 0 90000         ; 1 week, 1 hour, zero, 25 hours
   z=3730928400 -1h 3749680800 0 ; Sun 25-Mar-2018 1:00 UTC,
                                 ; offset 1 hour,
                                 ; Sun 28-Oct-2018 2:00 UTC,
                                 ; no offset
</pre><a href="#section-5.11-6" class="pilcrow">¶</a>
</div>
<p id="section-5.11-7">This specifies that at time 3730928400 (Sun 25-Mar-2018 1:00 UTC, 
        the onset of British Summer Time)  the time base by which the
        session's repeat times are calculated is shifted back by 1 hour, and
        that at time 3749680800 (Sun 28-Oct-2018 2:00 UTC, the end of British 
        Summer Time) the session's original time base is restored.
        Adjustments are always relative to the specified start time -- they
        are not cumulative.<a href="#section-5.11-7" class="pilcrow">¶</a></p>
<p id="section-5.11-8">If a session is likely to last several years, it is expected that
        the session description will be modified periodically rather than
        transmit several years' worth of adjustments in one session
        description.<a href="#section-5.11-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="key-field">
<section id="section-5.12">
        <h3 id="name-encryption-keys-k">
<a href="#section-5.12" class="section-number selfRef">5.12. </a><a href="#name-encryption-keys-k" class="section-name selfRef">Encryption Keys ("k=")</a>
        </h3>
<div id="section-5.12-1">
<pre class="sourcecode">
   k=&lt;method&gt;
   k=&lt;method&gt;:&lt;encryption key&gt;
</pre><a href="#section-5.12-1" class="pilcrow">¶</a>
</div>
<p id="section-5.12-2">The "k=" line (key-field) is obsolete and <span class="bcp14">MUST NOT</span> be used. It is included in 
            this document for legacy reasons. One <span class="bcp14">MUST NOT</span> include a "k=" line 
            in an SDP, and <span class="bcp14">MUST</span> discard it if it is received in an SDP.<a href="#section-5.12-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="attribspec">
<section id="section-5.13">
        <h3 id="name-attributes-a">
<a href="#section-5.13" class="section-number selfRef">5.13. </a><a href="#name-attributes-a" class="section-name selfRef">Attributes ("a=")</a>
        </h3>
<div id="section-5.13-1">
<pre class="sourcecode">
   a=&lt;attribute-name&gt;
   a=&lt;attribute-name&gt;:&lt;attribute-value&gt;
</pre><a href="#section-5.13-1" class="pilcrow">¶</a>
</div>
<p id="section-5.13-2">Attributes are the primary means for extending SDP. Attributes may
        be defined to be used as session-level attributes, media-level
        attributes, or both. (Attribute scopes in addition to media-level and
        session-level scopes may also be defined in extensions to this document,
        e.g., <span>[<a href="#RFC5576" class="xref">RFC5576</a>]</span> and  
        <span>[<a href="#RFC8864" class="xref">RFC8864</a>]</span>.)<a href="#section-5.13-2" class="pilcrow">¶</a></p>
<p id="section-5.13-3">A media description may contain any number of "a=" lines (attribute-fields)
        that are media description specific. These are referred to as media-level
        attributes and add information about the media description. Attribute-fields
        can also be added before the first media description; these session-level
        attributes convey additional information that applies to the session
        as a whole rather than to individual media descriptions.<a href="#section-5.13-3" class="pilcrow">¶</a></p>
<p id="section-5.13-4">Attribute-fields may be of two forms:<a href="#section-5.13-4" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-5.13-5.1">A property attribute is simply of the form "a=&lt;attribute-name&gt;".
            These are binary attributes, and the presence of the attribute
            conveys that the attribute is a property of the session. An
            example might be "a=recvonly".<a href="#section-5.13-5.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-5.13-5.2">A value attribute is of the form
            "a=&lt;attribute-name&gt;:&lt;attribute-value&gt;". For example, a whiteboard
            could have the value attribute "a=orient:landscape".<a href="#section-5.13-5.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-5.13-6">Attribute interpretation depends on the media tool being invoked.
        Thus receivers of session descriptions should be configurable in their
        interpretation of session descriptions in general and of attributes in
        particular.<a href="#section-5.13-6" class="pilcrow">¶</a></p>
<p id="section-5.13-7">Attribute names <span class="bcp14">MUST</span> use the US-ASCII subset of
        ISO-10646/UTF-8.<a href="#section-5.13-7" class="pilcrow">¶</a></p>
<p id="section-5.13-8">Attribute values are octet strings, and <span class="bcp14">MAY</span> use any octet value
        except 0x00 (Nul), 0x0A (LF), and 0x0D (CR). By default, attribute
        values are to be interpreted as in ISO-10646 character set with UTF-8
        encoding. Unlike other text fields, attribute values are NOT normally
        affected by the "a=charset:" attribute as this would make comparisons
        against known values problematic. However, when an attribute is
        defined, it can be defined to be charset dependent, in which case its
        value should be interpreted in the session charset rather than in
        ISO-10646.<a href="#section-5.13-8" class="pilcrow">¶</a></p>
<p id="section-5.13-9">Attributes <span class="bcp14">MUST</span> be registered with IANA (see <a href="#iana" class="xref">Section 8</a>). 
        If an attribute is received that is not understood,
        it <span class="bcp14">MUST</span> be ignored by the receiver.<a href="#section-5.13-9" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-5.14">
        <h3 id="name-media-descriptions-m">
<a href="#section-5.14" class="section-number selfRef">5.14. </a><a href="#name-media-descriptions-m" class="section-name selfRef">Media Descriptions ("m=")</a>
        </h3>
<div id="section-5.14-1">
<pre class="sourcecode">
   m=&lt;media&gt; &lt;port&gt; &lt;proto&gt; &lt;fmt&gt; ...
</pre><a href="#section-5.14-1" class="pilcrow">¶</a>
</div>
<p id="section-5.14-2">A session description may contain a number of media descriptions.
        Each media description starts with an "m=" line (media-field) and is terminated by
        either the next "m=" line or by the end of the session description. A
        media-field has several subfields:<a href="#section-5.14-2" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-5.14-3">
          <dt id="section-5.14-3.1">&lt;media&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.14-3.2">is the media type. This document defines the values "audio", "video", "text", "application", and "message". This list is extended by other memos and may be further extended by additional memos registering media types in the future (see <a href="#iana" class="xref">Section 8</a>). For example, <span>[<a href="#RFC6466" class="xref">RFC6466</a>]</span> defined the "image" media type.<a href="#section-5.14-3.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-5.14-3.3">&lt;port&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.14-3.4">
            <p id="section-5.14-3.4.1">is the transport port to which the
            media stream is sent. The meaning of the transport port depends on
            the network being used as specified in the relevant "c=" line, and
            on the transport protocol defined in the &lt;proto&gt; subfield
            of the media-field. Other ports used by the media application
            (such as the RTP Control Protocol (RTCP) port <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span>) <span class="bcp14">MAY</span> be derived algorithmically from the base
            media port or <span class="bcp14">MAY</span> be specified in a separate attribute (for
            example, the "a=rtcp:" attribute as defined in <span>[<a href="#RFC3605" class="xref">RFC3605</a>]</span>).<a href="#section-5.14-3.4.1" class="pilcrow">¶</a></p>
<p id="section-5.14-3.4.2">If noncontiguous ports are used or if they don't follow the
            parity rule of even RTP ports and odd RTCP ports, the "a=rtcp:"
            attribute <span class="bcp14">MUST</span> be used. Applications that are requested to send
            media to a &lt;port&gt; that is odd and where the "a=rtcp:" attribute is
            present <span class="bcp14">MUST NOT</span> subtract 1 from the RTP port: that is, they <span class="bcp14">MUST</span>
            send the RTP to the port indicated in &lt;port&gt; and send the
            RTCP to the port indicated in the "a=rtcp:" attribute.<a href="#section-5.14-3.4.2" class="pilcrow">¶</a></p>
<p id="section-5.14-3.4.3">For applications where hierarchically encoded streams are being
            sent to a unicast address, it may be necessary to specify multiple
            transport ports. This is done using a similar notation to that
            used for IP multicast addresses in the "c=" line:<a href="#section-5.14-3.4.3" class="pilcrow">¶</a></p>
<div id="section-5.14-3.4.4">
<pre class="sourcecode">
    m=&lt;media&gt; &lt;port&gt;/&lt;number of ports&gt; &lt;proto&gt; &lt;fmt&gt; ...
</pre><a href="#section-5.14-3.4.4" class="pilcrow">¶</a>
</div>
<p id="section-5.14-3.4.5">In such a case, the ports used depend on the transport
            protocol. For RTP, the default is that only the even-numbered
            ports are used for data with the corresponding one-higher odd
            ports used for the RTCP belonging to the RTP session, and the
            &lt;number of ports&gt; denoting the number of RTP sessions. For
            example:<a href="#section-5.14-3.4.5" class="pilcrow">¶</a></p>
<div id="section-5.14-3.4.6">
<pre class="sourcecode lang-sdp">
       m=video 49170/2 RTP/AVP 31
</pre><a href="#section-5.14-3.4.6" class="pilcrow">¶</a>
</div>
<p id="section-5.14-3.4.7">would specify that ports 49170 and 49171 form one RTP/RTCP pair,
            and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the
            transport protocol, and 31 is the format (see the description of &lt;fmt&gt; below).<a href="#section-5.14-3.4.7" class="pilcrow">¶</a></p>
<p id="section-5.14-3.4.8">This document does not include a mechanism for declaring hierarchically 
     encoded streams using noncontiguous ports.
     (There is currently no attribute defined that can accomplish this. 
     The "a=rtcp:" attribute defined in <span>[<a href="#RFC3605" class="xref">RFC3605</a>]</span> does not handle hierarchical encoding.)
     If a need arises to declare noncontiguous ports then it will be necessary to define a new attribute to do so.<a href="#section-5.14-3.4.8" class="pilcrow">¶</a></p>
<p id="section-5.14-3.4.9">If multiple addresses are specified in the "c=" line and
            multiple ports are specified in the "m=" line, a one-to-one
            mapping from port to the corresponding address is implied. For
            example:<a href="#section-5.14-3.4.9" class="pilcrow">¶</a></p>
<div id="section-5.14-3.4.10">
<pre class="sourcecode lang-sdp">
       m=video 49170/2 RTP/AVP 31
       c=IN IP4 233.252.0.1/127/2
</pre><a href="#section-5.14-3.4.10" class="pilcrow">¶</a>
</div>
<p id="section-5.14-3.4.11">would imply that address 233.252.0.1 is used with ports 49170
            and 49171, and address 233.252.0.2 is used with ports 49172 and
            49173.<a href="#section-5.14-3.4.11" class="pilcrow">¶</a></p>
<p id="section-5.14-3.4.12">The mapping is similar if multiple addresses are specified using multiple "c=" lines.
            For example:<a href="#section-5.14-3.4.12" class="pilcrow">¶</a></p>
<div id="section-5.14-3.4.13">
<pre class="sourcecode lang-sdp">
       m=video 49170/2 RTP/AVP 31
       c=IN IP6 ff00::db8:0:101
       c=IN IP6 ff00::db8:0:102
</pre><a href="#section-5.14-3.4.13" class="pilcrow">¶</a>
</div>
<p id="section-5.14-3.4.14">would imply that address ff00::db8:0:101 is used with ports 49170
            and 49171, and address ff00::db8:0:102 is used with ports 49172 and
            49173.<a href="#section-5.14-3.4.14" class="pilcrow">¶</a></p>
<p id="section-5.14-3.4.15">This document gives no meaning to assigning the same media address to 
     multiple media descriptions. 
     Doing so does not implicitly group those media descriptions in any way.
     An explicit grouping framework (for example, <span>[<a href="#RFC5888" class="xref">RFC5888</a>]</span>) 
     should instead be used to express the intended semantics. 
     For instance, see <span>[<a href="#RFC8843" class="xref">RFC8843</a>]</span>.<a href="#section-5.14-3.4.15" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-5.14-3.5">&lt;proto&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.14-3.6">
            <p id="section-5.14-3.6.1">is the transport protocol. The meaning
            of the transport protocol is dependent on the address type subfield
            in the relevant "c=" line. Thus a "c=" line with an address type of "IP4" indicates that
            the transport protocol runs over IPv4. The following transport
            protocols are defined, but may be extended through registration of
            new protocols with IANA (see <a href="#iana" class="xref">Section 8</a>):<a href="#section-5.14-3.6.1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-5.14-3.6.2.1">udp: denotes that the data is transported directly in UDP 
                with no additional framing.<a href="#section-5.14-3.6.2.1" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-5.14-3.6.2.2">RTP/AVP: denotes <span><a href="#RFC3550" class="xref">RTP</a> [<a href="#RFC3550" class="xref">RFC3550</a>]</span> used
                under the <span><a href="#RFC3551" class="xref">RTP Profile for Audio and
                Video Conferences with Minimal Control</a> [<a href="#RFC3551" class="xref">RFC3551</a>]</span> running over
                UDP.<a href="#section-5.14-3.6.2.2" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-5.14-3.6.2.3">RTP/SAVP: denotes the <span><a href="#RFC3711" class="xref">Secure
                Real-time Transport Protocol</a> [<a href="#RFC3711" class="xref">RFC3711</a>]</span> running over UDP.<a href="#section-5.14-3.6.2.3" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-5.14-3.6.2.4">RTP/SAVPF: denotes SRTP with the <span><a href="#RFC5124" class="xref">Extended SRTP Profile for RTCP-Based Feedback</a> [<a href="#RFC5124" class="xref">RFC5124</a>]</span> running over UDP.<a href="#section-5.14-3.6.2.4" class="pilcrow">¶</a>
</li>
            </ul>
<p id="section-5.14-3.6.3">The main reason to specify the transport protocol in addition
            to the media format is that the same standard media formats may be
            carried over different transport protocols even when the network
            protocol is the same -- a historical example is vat (MBone's popular multimedia audio tool) Pulse Code
            Modulation (PCM) audio and RTP PCM audio; another might be TCP/RTP
            PCM audio. In addition, relays and monitoring tools that are
            transport-protocol-specific but format-independent are
            possible.<a href="#section-5.14-3.6.3" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-5.14-3.7">&lt;fmt&gt;</dt>
          <dd style="margin-left: 1.5em" id="section-5.14-3.8">
            <p id="section-5.14-3.8.1">is a media format description. The
            fourth and any subsequent subfields describe the format of the
            media. The interpretation of the media format depends on the value
            of the &lt;proto&gt; subfield.<a href="#section-5.14-3.8.1" class="pilcrow">¶</a></p>
<p id="section-5.14-3.8.2">If the &lt;proto&gt; subfield is "RTP/AVP" or "RTP/SAVP", the
            &lt;fmt&gt; subfields contain RTP payload type numbers.  When a list of 
payload type numbers is given, this implies that all of these 
payload formats MAY be used in the session, and these payload 
formats are listed in order of preference, with the first format listed 
being preferred. When multiple payload formats are listed,
the first acceptable payload format 
from the beginning of the list <span class="bcp14">SHOULD</span> be used for the session.

            For dynamic payload type assignments, the "a=rtpmap:"
            attribute (see <a href="#rtpmap" class="xref">Section 6.6</a>) <span class="bcp14">SHOULD</span> be used to map from
            an RTP payload type number to a media encoding name that
            identifies the payload format. The "a=fmtp:" attribute <span class="bcp14">MAY</span> be used
            to specify format parameters (see <a href="#fmtp" class="xref">Section 6.15</a>).<a href="#section-5.14-3.8.2" class="pilcrow">¶</a></p>
<p id="section-5.14-3.8.3">If the &lt;proto&gt; subfield is "udp", the &lt;fmt&gt;
            subfields <span class="bcp14">MUST</span> reference a media type describing the format under
            the "audio", "video", "text", "application", or "message"
            top-level media types. The media type registration <span class="bcp14">SHOULD</span> define
            the packet format for use with UDP transport.<a href="#section-5.14-3.8.3" class="pilcrow">¶</a></p>
<p id="section-5.14-3.8.4">For media using other transport protocols, the &lt;fmt&gt;
            subfield is protocol specific. Rules for interpretation of the
            &lt;fmt&gt; subfield <span class="bcp14">MUST</span> be defined when registering new
            protocols (see <a href="#MediaTypes" class="xref">Section 8.2.2</a>).<a href="#section-5.14-3.8.4" class="pilcrow">¶</a></p>
<p id="section-5.14-3.8.5"><span><a href="https://www.rfc-editor.org/rfc/rfc4855#section-3" class="relref">Section 3</a> of [<a href="#RFC4855" class="xref">RFC4855</a>]</span> states that the payload
            format (encoding) names defined in the RTP profile are commonly
            shown in upper case, while media subtype names are commonly shown
            in lower case. It also states that both of these names are
            case-insensitive in both places, similar to parameter names which
            are case-insensitive both in media type strings and in the default
            mapping to the SDP "a=fmtp:" attribute.<a href="#section-5.14-3.8.5" class="pilcrow">¶</a></p>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</section>
</div>
<div id="attrs">
<section id="section-6">
      <h2 id="name-sdp-attributes">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-sdp-attributes" class="section-name selfRef">SDP Attributes</a>
      </h2>
<p id="section-6-1">The following attributes are defined. Since application writers may
      add new attributes as they are required, this list is not exhaustive.
      Registration procedures for new attributes are defined in <a href="#AttributeNames" class="xref">Section 8.2.4</a>. 
      Syntax is provided using ABNF <span>[<a href="#RFC7405" class="xref">RFC7405</a>]</span> 
      with some of the rules defined further in <a href="#abnf" class="xref">Section 9</a>.<a href="#section-6-1" class="pilcrow">¶</a></p>
<div id="cat">
<section id="section-6.1">
        <h3 id="name-cat-category">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-cat-category" class="section-name selfRef">cat (Category)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.1-1">
          <dt id="section-6.1-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.2">cat<a href="#section-6.1-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.4">cat-value<a href="#section-6.1-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.6">session<a href="#section-6.1-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.8">no<a href="#section-6.1-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.1-2">Syntax:<a href="#section-6.1-2" class="pilcrow">¶</a></p>
<div id="section-6.1-3">
<pre class="sourcecode lang-abnf">
      cat-value = category
      category = non-ws-string
</pre><a href="#section-6.1-3" class="pilcrow">¶</a>
</div>
<p id="section-6.1-4">Example:<a href="#section-6.1-4" class="pilcrow">¶</a></p>
<div id="section-6.1-5">
<pre class="sourcecode lang-sdp">
      a=cat:foo.bar
</pre><a href="#section-6.1-5" class="pilcrow">¶</a>
</div>
<p id="section-6.1-6">This attribute gives the dot-separated hierarchical category of the
        session. This is to enable a receiver to filter unwanted sessions by
        category. There is no central registry of categories. This attribute
        is obsolete and <span class="bcp14">SHOULD NOT</span> be used. It <span class="bcp14">SHOULD</span> be ignored if received.<a href="#section-6.1-6" class="pilcrow">¶</a></p>
</section>
</div>
<div id="keywds">
<section id="section-6.2">
        <h3 id="name-keywds-keywords">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-keywds-keywords" class="section-name selfRef">keywds (Keywords)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.2-1">
          <dt id="section-6.2-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.2">keywds<a href="#section-6.2-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.2-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.4">keywds-value<a href="#section-6.2-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.2-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.6">session<a href="#section-6.2-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.2-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.8">yes<a href="#section-6.2-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.2-2">Syntax:<a href="#section-6.2-2" class="pilcrow">¶</a></p>
<div id="section-6.2-3">
<pre class="sourcecode lang-abnf">
      keywds-value = keywords
      keywords = text
</pre><a href="#section-6.2-3" class="pilcrow">¶</a>
</div>
<p id="section-6.2-4">Example:<a href="#section-6.2-4" class="pilcrow">¶</a></p>
<div id="section-6.2-5">
<pre class="sourcecode lang-sdp">
      a=keywds:SDP session description protocol
</pre><a href="#section-6.2-5" class="pilcrow">¶</a>
</div>
<p id="section-6.2-6">Like the "a=cat:" attribute, this was intended to assist identifying wanted
        sessions at the receiver, and to allow a receiver to select interesting
        sessions based on keywords describing the purpose of the session; however, there
        is no central registry of keywords. Its value should be interpreted in
        the charset specified for the session description if one is specified,
        or by default in ISO 10646/UTF-8. This attribute is obsolete and 
 <span class="bcp14">SHOULD NOT</span> be used. It <span class="bcp14">SHOULD</span> be ignored if received.<a href="#section-6.2-6" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-6.3">
        <h3 id="name-tool">
<a href="#section-6.3" class="section-number selfRef">6.3. </a><a href="#name-tool" class="section-name selfRef">tool</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.3-1">
          <dt id="section-6.3-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.3-1.2">tool<a href="#section-6.3-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.3-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.3-1.4">tool-value<a href="#section-6.3-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.3-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.3-1.6">session<a href="#section-6.3-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.3-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.3-1.8">no<a href="#section-6.3-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.3-2">Syntax:<a href="#section-6.3-2" class="pilcrow">¶</a></p>
<div id="section-6.3-3">
<pre class="sourcecode lang-abnf">
      tool-value = tool-name-and-version
      tool-name-and-version = text
</pre><a href="#section-6.3-3" class="pilcrow">¶</a>
</div>
<p id="section-6.3-4">Example:<a href="#section-6.3-4" class="pilcrow">¶</a></p>
<div id="section-6.3-5">
<pre class="sourcecode lang-sdp">
      a=tool:foobar V3.2
</pre><a href="#section-6.3-5" class="pilcrow">¶</a>
</div>
<p id="section-6.3-6">This gives the name and version number of the tool used to create
        the session description.<a href="#section-6.3-6" class="pilcrow">¶</a></p>
</section>
<div id="ptime">
<section id="section-6.4">
        <h3 id="name-ptime-packet-time">
<a href="#section-6.4" class="section-number selfRef">6.4. </a><a href="#name-ptime-packet-time" class="section-name selfRef">ptime (Packet Time)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.4-1">
          <dt id="section-6.4-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.4-1.2">ptime<a href="#section-6.4-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.4-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.4-1.4">ptime-value<a href="#section-6.4-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.4-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.4-1.6">media<a href="#section-6.4-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.4-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.4-1.8">no<a href="#section-6.4-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.4-2">Syntax:<a href="#section-6.4-2" class="pilcrow">¶</a></p>
<div id="section-6.4-3">
<pre class="sourcecode lang-abnf">
      ptime-value = non-zero-int-or-real
</pre><a href="#section-6.4-3" class="pilcrow">¶</a>
</div>
<p id="section-6.4-4">Example:<a href="#section-6.4-4" class="pilcrow">¶</a></p>
<div id="section-6.4-5">
<pre class="sourcecode lang-sdp">
      a=ptime:20
</pre><a href="#section-6.4-5" class="pilcrow">¶</a>
</div>
<p id="section-6.4-6">This gives the length of time in milliseconds represented by the
        media in a packet. This is probably only meaningful for audio data,
        but may be used with other media types if it makes sense. It should
        not be necessary to know "a=ptime:" to decode RTP or vat audio, and it is
        intended as a recommendation for the encoding/packetization of
        audio.<a href="#section-6.4-6" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-6.5">
        <h3 id="name-maxptime-maximum-packet-tim">
<a href="#section-6.5" class="section-number selfRef">6.5. </a><a href="#name-maxptime-maximum-packet-tim" class="section-name selfRef">maxptime (Maximum Packet Time)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.5-1">
          <dt id="section-6.5-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.5-1.2">maxptime<a href="#section-6.5-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.5-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.5-1.4">maxptime-value<a href="#section-6.5-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.5-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.5-1.6">media<a href="#section-6.5-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.5-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.5-1.8">no<a href="#section-6.5-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.5-2">Syntax:<a href="#section-6.5-2" class="pilcrow">¶</a></p>
<div id="section-6.5-3">
<pre class="sourcecode lang-abnf">
      maxptime-value = non-zero-int-or-real
</pre><a href="#section-6.5-3" class="pilcrow">¶</a>
</div>
<p id="section-6.5-4">Example:<a href="#section-6.5-4" class="pilcrow">¶</a></p>
<div id="section-6.5-5">
<pre class="sourcecode lang-sdp">
      a=maxptime:20
</pre><a href="#section-6.5-5" class="pilcrow">¶</a>
</div>
<p id="section-6.5-6">This gives the maximum amount of media that can be encapsulated in
        each packet, expressed as time in milliseconds. The time <span class="bcp14">SHALL</span> be
        calculated as the sum of the time the media present in the packet
        represents. For frame-based codecs, the time <span class="bcp14">SHOULD</span> be an integer
        multiple of the frame size. This attribute is probably only meaningful
        for audio data, but may be used with other media types if it makes
        sense. Note that this attribute was introduced after <span>[<a href="#RFC2327" class="xref">RFC2327</a>]</span>, 
        and implementations that have not been updated will ignore this
        attribute.<a href="#section-6.5-6" class="pilcrow">¶</a></p>
</section>
<div id="rtpmap">
<section id="section-6.6">
        <h3 id="name-rtpmap">
<a href="#section-6.6" class="section-number selfRef">6.6. </a><a href="#name-rtpmap" class="section-name selfRef">rtpmap</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.6-1">
          <dt id="section-6.6-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.6-1.2">rtpmap<a href="#section-6.6-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.6-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.6-1.4">rtpmap-value<a href="#section-6.6-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.6-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.6-1.6">media<a href="#section-6.6-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.6-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.6-1.8">no<a href="#section-6.6-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.6-2">Syntax:<a href="#section-6.6-2" class="pilcrow">¶</a></p>
<div id="section-6.6-3">
<pre class="sourcecode lang-abnf">
      rtpmap-value = payload-type SP encoding-name
        "/" clock-rate [ "/" encoding-params ]
      payload-type = zero-based-integer
      encoding-name = token
      clock-rate = integer
      encoding-params = channels
      channels = integer
</pre><a href="#section-6.6-3" class="pilcrow">¶</a>
</div>
<p id="section-6.6-4">This attribute maps from an RTP payload type number (as used in an
        "m=" line) to an encoding name denoting the payload format to be used.
        It also provides information on the clock rate and encoding
        parameters. Note that the payload type number is indicated in a 7-bit
        field, limiting the values to inclusively between 0 and 127.<a href="#section-6.6-4" class="pilcrow">¶</a></p>
<p id="section-6.6-5">Although an RTP profile can make static assignments of payload type
        numbers to payload formats, it is more common for that assignment to
        be done dynamically using "a=rtpmap:" attributes. As an example of a
        static payload type, consider u-law PCM encoded single-channel audio
        sampled at 8 kHz. This is completely defined in the RTP audio/video
        profile as payload type 0, so there is no need for an "a=rtpmap:"
        attribute, and the media for such a stream sent to UDP port 49232 can
        be specified as:<a href="#section-6.6-5" class="pilcrow">¶</a></p>
<div id="section-6.6-6">
<pre class="sourcecode lang-sdp">
          m=audio 49232 RTP/AVP 0
</pre><a href="#section-6.6-6" class="pilcrow">¶</a>
</div>
<p id="section-6.6-7">An example of a dynamic payload type is 16-bit linear encoded
        stereo audio sampled at 16 kHz. If we wish to use the dynamic RTP/AVP
        payload type 98 for this stream, additional information is required to
        decode it:<a href="#section-6.6-7" class="pilcrow">¶</a></p>
<div id="section-6.6-8">
<pre class="sourcecode lang-sdp">
          m=audio 49232 RTP/AVP 98
          a=rtpmap:98 L16/16000/2
</pre><a href="#section-6.6-8" class="pilcrow">¶</a>
</div>
<p id="section-6.6-9">Up to one "a=rtpmap:" attribute can be defined for each media format
        specified. Thus, we might have the following:<a href="#section-6.6-9" class="pilcrow">¶</a></p>
<div id="section-6.6-10">
<pre class="sourcecode lang-sdp">
          m=audio 49230 RTP/AVP 96 97 98
          a=rtpmap:96 L8/8000
          a=rtpmap:97 L16/8000
          a=rtpmap:98 L16/11025/2
</pre><a href="#section-6.6-10" class="pilcrow">¶</a>
</div>
<p id="section-6.6-11">RTP profiles that specify the use of dynamic payload types <span class="bcp14">MUST</span>
        define the set of valid encoding names and/or a means to register
        encoding names if that profile is to be used with SDP. The "RTP/AVP"
        and "RTP/SAVP" profiles use media subtypes for encoding names, under
        the top-level media type denoted in the "m=" line. In the example
        above, the media types are "audio/L8" and "audio/L16".<a href="#section-6.6-11" class="pilcrow">¶</a></p>
<p id="section-6.6-12">For audio streams, encoding-params indicates the number
        of audio channels. This parameter is <span class="bcp14">OPTIONAL</span> and may be omitted if
        the number of channels is one, provided that no additional parameters
        are needed.<a href="#section-6.6-12" class="pilcrow">¶</a></p>
<p id="section-6.6-13">For video streams, no encoding parameters are currently
        specified.<a href="#section-6.6-13" class="pilcrow">¶</a></p>
<p id="section-6.6-14">Additional encoding parameters <span class="bcp14">MAY</span> be defined in the future, but
        codec-specific parameters <span class="bcp14">SHOULD NOT</span> be added. Parameters added to an
        "a=rtpmap:" attribute <span class="bcp14">SHOULD</span> only be those required for a session
        directory to make the choice of appropriate media to participate in a
        session. Codec-specific parameters should be added in other attributes
        (for example, "a=fmtp:").<a href="#section-6.6-14" class="pilcrow">¶</a></p>
<p id="section-6.6-15">Note: RTP audio formats typically do not include information about
        the number of samples per packet. If a non-default (as defined in the
        RTP Audio/Video Profile <span>[<a href="#RFC3551" class="xref">RFC3551</a>]</span>) packetization is required, the "a=ptime:"
        attribute is used as given in <a href="#ptime" class="xref">Section 6.4</a>.<a href="#section-6.6-15" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-6.7">
        <h3 id="name-media-direction-attributes">
<a href="#section-6.7" class="section-number selfRef">6.7. </a><a href="#name-media-direction-attributes" class="section-name selfRef">Media Direction Attributes</a>
        </h3>
<p id="section-6.7-1">At most one occurrence of "a=recvonly", "a=sendrecv", "a=sendonly", 
        or "a=inactive" <span class="bcp14">MAY</span> appear at
        session level, and at most one <span class="bcp14">MAY</span> appear in each media description.<a href="#section-6.7-1" class="pilcrow">¶</a></p>
<p id="section-6.7-2">If any one of these appears in a media description, then it applies for
        that media description. If none appears in a media description, then the one
        from session level, if any, applies to that media description.<a href="#section-6.7-2" class="pilcrow">¶</a></p>
<p id="section-6.7-3">If none of the media direction attributes is present at either
        session level or media level, "a=sendrecv" <span class="bcp14">SHOULD</span> be assumed as the
        default.<a href="#section-6.7-3" class="pilcrow">¶</a></p>
<p id="section-6.7-4">Within the following SDP example, the "a=sendrecv" attribute applies 
        to the first audio media and the "a=inactive" attribute applies to the others.<a href="#section-6.7-4" class="pilcrow">¶</a></p>
<div id="section-6.7-5">
<pre class="sourcecode lang-sdp">
      v=0
      o=jdoe 3724395000 3724395001 IN IP6 2001:db8::1
      s=-
      c=IN IP6 2001:db8::1
      t=0 0
      a=inactive
      m=audio 49170 RTP/AVP 0
      a=sendrecv
      m=audio 49180 RTP/AVP 0
      m=video 51372 RTP/AVP 99
      a=rtpmap:99 h263-1998/90000
</pre><a href="#section-6.7-5" class="pilcrow">¶</a>
</div>
<section id="section-6.7.1">
          <h4 id="name-recvonly-receive-only">
<a href="#section-6.7.1" class="section-number selfRef">6.7.1. </a><a href="#name-recvonly-receive-only" class="section-name selfRef">recvonly (Receive-Only)</a>
          </h4>
<span class="break"></span><dl class="dlParallel" id="section-6.7.1-1">
            <dt id="section-6.7.1-1.1">Name:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.1-1.2">recvonly<a href="#section-6.7.1-1.2" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.1-1.3">Value:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.1-1.4"></dd>
            <dd class="break"></dd>
<dt id="section-6.7.1-1.5">Usage Level:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.1-1.6">session, media<a href="#section-6.7.1-1.6" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.1-1.7">Charset Dependent:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.1-1.8">no<a href="#section-6.7.1-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
</dl>
<p id="section-6.7.1-2">Example:<a href="#section-6.7.1-2" class="pilcrow">¶</a></p>
<div id="section-6.7.1-3">
<pre class="sourcecode lang-sdp">
      a=recvonly
</pre><a href="#section-6.7.1-3" class="pilcrow">¶</a>
</div>
<p id="section-6.7.1-4">This specifies that the tools should be started in receive-only
          mode where applicable. Note that receive-only mode applies to the media only,
          not to any associated control protocol. 
          An RTP-based system in receive-only mode <span class="bcp14">MUST</span> still send RTCP packets 
          as described in <span>[<a href="#RFC3550" class="xref">RFC3550</a>], <a href="https://www.rfc-editor.org/rfc/rfc3550#section-6" class="relref">Section 6</a></span>.<a href="#section-6.7.1-4" class="pilcrow">¶</a></p>
</section>
<section id="section-6.7.2">
          <h4 id="name-sendrecv-send-receive">
<a href="#section-6.7.2" class="section-number selfRef">6.7.2. </a><a href="#name-sendrecv-send-receive" class="section-name selfRef">sendrecv (Send-Receive)</a>
          </h4>
<span class="break"></span><dl class="dlParallel" id="section-6.7.2-1">
            <dt id="section-6.7.2-1.1">Name:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.2-1.2">sendrecv<a href="#section-6.7.2-1.2" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.2-1.3">Value:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.2-1.4"></dd>
            <dd class="break"></dd>
<dt id="section-6.7.2-1.5">Usage Level:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.2-1.6">session, media<a href="#section-6.7.2-1.6" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.2-1.7">Charset Dependent:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.2-1.8">no<a href="#section-6.7.2-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
</dl>
<p id="section-6.7.2-2">Example:<a href="#section-6.7.2-2" class="pilcrow">¶</a></p>
<div id="section-6.7.2-3">
<pre class="sourcecode lang-sdp">
      a=sendrecv
</pre><a href="#section-6.7.2-3" class="pilcrow">¶</a>
</div>
<p id="section-6.7.2-4">This specifies that the tools should be started in send and
          receive mode. This is necessary for interactive multimedia
          conferences with tools that default to receive-only mode.<a href="#section-6.7.2-4" class="pilcrow">¶</a></p>
</section>
<section id="section-6.7.3">
          <h4 id="name-sendonly-send-only">
<a href="#section-6.7.3" class="section-number selfRef">6.7.3. </a><a href="#name-sendonly-send-only" class="section-name selfRef">sendonly (Send-Only)</a>
          </h4>
<span class="break"></span><dl class="dlParallel" id="section-6.7.3-1">
            <dt id="section-6.7.3-1.1">Name:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.3-1.2">sendonly<a href="#section-6.7.3-1.2" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.3-1.3">Value:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.3-1.4"></dd>
            <dd class="break"></dd>
<dt id="section-6.7.3-1.5">Usage Level:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.3-1.6">session, media<a href="#section-6.7.3-1.6" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.3-1.7">Charset Dependent:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.3-1.8">no<a href="#section-6.7.3-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
</dl>
<p id="section-6.7.3-2">Example:<a href="#section-6.7.3-2" class="pilcrow">¶</a></p>
<div id="section-6.7.3-3">
<pre class="sourcecode lang-sdp">
      a=sendonly
</pre><a href="#section-6.7.3-3" class="pilcrow">¶</a>
</div>
<p id="section-6.7.3-4">This specifies that the tools should be started in send-only
          mode. An example may be where a different unicast address is to be
          used for a traffic destination than for a traffic source. In such a
          case, two media descriptions may be used, one in send-only mode and one
          in receive-vonly mode. Note that send-only mode applies only to the media, and any
          associated control protocol (e.g., RTCP) <span class="bcp14">SHOULD</span> still be received
          and processed as normal.<a href="#section-6.7.3-4" class="pilcrow">¶</a></p>
</section>
<div id="inactive">
<section id="section-6.7.4">
          <h4 id="name-inactive">
<a href="#section-6.7.4" class="section-number selfRef">6.7.4. </a><a href="#name-inactive" class="section-name selfRef">inactive</a>
          </h4>
<span class="break"></span><dl class="dlParallel" id="section-6.7.4-1">
            <dt id="section-6.7.4-1.1">Name:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.4-1.2">inactive<a href="#section-6.7.4-1.2" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.4-1.3">Value:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.4-1.4"></dd>
            <dd class="break"></dd>
<dt id="section-6.7.4-1.5">Usage Level:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.4-1.6">session, media<a href="#section-6.7.4-1.6" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
<dt id="section-6.7.4-1.7">Charset Dependent:</dt>
            <dd style="margin-left: 1.5em" id="section-6.7.4-1.8">no<a href="#section-6.7.4-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
</dl>
<p id="section-6.7.4-2">Example:<a href="#section-6.7.4-2" class="pilcrow">¶</a></p>
<div id="section-6.7.4-3">
<pre class="sourcecode lang-sdp">
      a=inactive
</pre><a href="#section-6.7.4-3" class="pilcrow">¶</a>
</div>
<p id="section-6.7.4-4">This specifies that the tools should be started in inactive mode.
          This is necessary for interactive multimedia conferences where users
          can put other users on hold. No media is sent over an inactive media
          stream. Note that an RTP-based system <span class="bcp14">MUST</span> still send RTCP (if RTCP
          is used), even if started in inactive mode.<a href="#section-6.7.4-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
<section id="section-6.8">
        <h3 id="name-orient-orientation">
<a href="#section-6.8" class="section-number selfRef">6.8. </a><a href="#name-orient-orientation" class="section-name selfRef">orient (Orientation)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.8-1">
          <dt id="section-6.8-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.8-1.2">orient<a href="#section-6.8-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.8-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.8-1.4">orient-value<a href="#section-6.8-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.8-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.8-1.6">media<a href="#section-6.8-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.8-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.8-1.8">no<a href="#section-6.8-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.8-2">Syntax:<a href="#section-6.8-2" class="pilcrow">¶</a></p>
<div id="section-6.8-3">
<pre class="sourcecode lang-abnf">
      orient-value = portrait / landscape / seascape
      portrait  = %s"portrait"
      landscape = %s"landscape"
      seascape  = %s"seascape"
         ; NOTE: These names are case-sensitive.
</pre><a href="#section-6.8-3" class="pilcrow">¶</a>
</div>
<p id="section-6.8-4">Example:<a href="#section-6.8-4" class="pilcrow">¶</a></p>
<div id="section-6.8-5">
<pre class="sourcecode lang-sdp">
      a=orient:portrait
</pre><a href="#section-6.8-5" class="pilcrow">¶</a>
</div>
<p id="section-6.8-6">Normally this is only used for a whiteboard or presentation tool.
        It specifies the orientation of the workspace on the screen.
        Permitted values are "portrait", "landscape", and "seascape"
        (upside-down landscape).<a href="#section-6.8-6" class="pilcrow">¶</a></p>
</section>
<div id="type">
<section id="section-6.9">
        <h3 id="name-type-conference-type">
<a href="#section-6.9" class="section-number selfRef">6.9. </a><a href="#name-type-conference-type" class="section-name selfRef">type (Conference Type)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.9-1">
          <dt id="section-6.9-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.9-1.2">type<a href="#section-6.9-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.9-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.9-1.4">type-value<a href="#section-6.9-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.9-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.9-1.6">session<a href="#section-6.9-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.9-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.9-1.8">no<a href="#section-6.9-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.9-2">Syntax:<a href="#section-6.9-2" class="pilcrow">¶</a></p>
<div id="section-6.9-3">
<pre class="sourcecode lang-abnf">
      type-value = conference-type
      conference-type = broadcast / meeting / moderated / test /
                        H332
      broadcast = %s"broadcast"
      meeting   = %s"meeting"
      moderated = %s"moderated"
      test      = %s"test"
      H332      = %s"H332"
         ; NOTE: These names are case-sensitive.
</pre><a href="#section-6.9-3" class="pilcrow">¶</a>
</div>
<p id="section-6.9-4">Example:<a href="#section-6.9-4" class="pilcrow">¶</a></p>
<div id="section-6.9-5">
<pre class="sourcecode lang-sdp">
      a=type:moderated
</pre><a href="#section-6.9-5" class="pilcrow">¶</a>
</div>
<p id="section-6.9-6">This specifies the type of the multimedia conference. 
        Allowed values are "broadcast", "meeting", "moderated", "test", and "H332".
        These values have implications for other options that are likely to be appropriate:<a href="#section-6.9-6" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-6.9-7.1">When "a=type:broadcast" is specified, "a=recvonly" is probably
                 appropriate for those connecting.<a href="#section-6.9-7.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-6.9-7.2">When "a=type:meeting" is specified, "a=sendrecv" is likely to be appropriate.<a href="#section-6.9-7.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-6.9-7.3">"a=type:moderated" suggests the use of a floor control tool and 
                 that the media tools be started so as to mute new sites joining the 
                 multimedia conference.<a href="#section-6.9-7.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-6.9-7.4">Specifying "a=type:H332" indicates that this loosely
                 coupled session is part of an H.332 session as defined in the ITU
                 H.332 specification <span>[<a href="#ITU.H332.1998" class="xref">ITU.H332.1998</a>]</span>. Media tools should
                 be started using "a=recvonly".<a href="#section-6.9-7.4" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-6.9-7.5">Specifying "a=type:test" is suggested as a hint that,
                 unless explicitly requested otherwise, receivers can safely avoid
                 displaying this session description to users.<a href="#section-6.9-7.5" class="pilcrow">¶</a>
</li>
        </ul>
</section>
</div>
<div id="charset">
<section id="section-6.10">
        <h3 id="name-charset-character-set">
<a href="#section-6.10" class="section-number selfRef">6.10. </a><a href="#name-charset-character-set" class="section-name selfRef">charset (Character Set)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.10-1">
          <dt id="section-6.10-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.10-1.2">charset<a href="#section-6.10-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.10-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.10-1.4">charset-value<a href="#section-6.10-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.10-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.10-1.6">session<a href="#section-6.10-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.10-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.10-1.8">no<a href="#section-6.10-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.10-2">Syntax:<a href="#section-6.10-2" class="pilcrow">¶</a></p>
<div id="section-6.10-3">
<pre class="sourcecode lang-abnf">
      charset-value = &lt;defined in [RFC2978]&gt;
</pre><a href="#section-6.10-3" class="pilcrow">¶</a>
</div>
<p id="section-6.10-4">This specifies the character set to be used to display the session
        name and information data. By default, the ISO-10646 character set in
        UTF-8 encoding is used. If a more compact representation is required,
        other character sets may be used. For example, the ISO 8859-1 is
        specified with the following SDP attribute:<a href="#section-6.10-4" class="pilcrow">¶</a></p>
<div id="section-6.10-5">
<pre class="sourcecode lang-sdp">
      a=charset:ISO-8859-1
</pre><a href="#section-6.10-5" class="pilcrow">¶</a>
</div>
<p id="section-6.10-6">The charset specified <span class="bcp14">MUST</span> be one of those registered in the IANA
        Character Sets registry
        (<span><a href="http://www.iana.org/assignments/character-sets">http://www.iana.org/assignments/character-sets</a></span>), such as ISO-8859-1.
        The character set identifier is a string that <span class="bcp14">MUST</span> be compared
        against identifiers from the "Name" or "Preferred MIME Name" field of
        the registry using a case-insensitive comparison. If the identifier is
        not recognized or not supported, all strings that are affected by it
        <span class="bcp14">SHOULD</span> be regarded as octet strings.<a href="#section-6.10-6" class="pilcrow">¶</a></p>
<p id="section-6.10-7">Charset-dependent fields <span class="bcp14">MUST</span> contain only sequences of bytes that are
        valid according to the definition of the selected character set.
        Furthermore, charset-dependent fields <span class="bcp14">MUST NOT</span> contain the bytes 0x00 (Nul), 
        0x0A (LF), and 0x0d (CR).<a href="#section-6.10-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="sdplang">
<section id="section-6.11">
        <h3 id="name-sdplang-sdp-language">
<a href="#section-6.11" class="section-number selfRef">6.11. </a><a href="#name-sdplang-sdp-language" class="section-name selfRef">sdplang (SDP Language)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.11-1">
          <dt id="section-6.11-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.11-1.2">sdplang<a href="#section-6.11-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.11-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.11-1.4">sdplang-value<a href="#section-6.11-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.11-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.11-1.6">session, media<a href="#section-6.11-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.11-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.11-1.8">no<a href="#section-6.11-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.11-2">Syntax:<a href="#section-6.11-2" class="pilcrow">¶</a></p>
<div id="section-6.11-3">
<pre class="sourcecode lang-abnf">
      sdplang-value = Language-Tag
      ; Language-Tag defined in RFC 5646
</pre><a href="#section-6.11-3" class="pilcrow">¶</a>
</div>
<p id="section-6.11-4">Example:<a href="#section-6.11-4" class="pilcrow">¶</a></p>
<div id="section-6.11-5">
<pre class="sourcecode lang-sdp">
      a=sdplang:fr
</pre><a href="#section-6.11-5" class="pilcrow">¶</a>
</div>
<p id="section-6.11-6">Multiple "a=sdplang:" attributes can be provided either at session or
        media level if the session description or media use multiple
        languages.<a href="#section-6.11-6" class="pilcrow">¶</a></p>
<p id="section-6.11-7">As a session-level attribute, it specifies the language for the
        session description (not the language of the media). As a media-level
        attribute, it specifies the language for any media-level SDP
        information-field associated with that media (again not the language
        of the media), overriding any "a=sdplang:" attributes specified at
        session level.<a href="#section-6.11-7" class="pilcrow">¶</a></p>
<p id="section-6.11-8">In general, sending session descriptions consisting of multiple
        languages is discouraged. Instead, multiple session descriptions <span class="bcp14">SHOULD</span> be
        sent describing the session, one in each language. However, this is
        not possible with all transport mechanisms, and so multiple "a=sdplang:"
        attributes are allowed although <span class="bcp14">NOT RECOMMENDED</span>.<a href="#section-6.11-8" class="pilcrow">¶</a></p>
<p id="section-6.11-9">The "a=sdplang:" attribute value must be a single language tag
        <span>[<a href="#RFC5646" class="xref">RFC5646</a>]</span>. An "a=sdplang:" attribute
        <span class="bcp14">SHOULD</span> be specified when a session is distributed with sufficient
        scope to cross geographic boundaries, where the language of recipients
        cannot be assumed, or where the session is in a different language
        from the locally assumed norm.<a href="#section-6.11-9" class="pilcrow">¶</a></p>
</section>
</div>
<div id="lang">
<section id="section-6.12">
        <h3 id="name-lang-language">
<a href="#section-6.12" class="section-number selfRef">6.12. </a><a href="#name-lang-language" class="section-name selfRef">lang (Language)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.12-1">
          <dt id="section-6.12-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.12-1.2">lang<a href="#section-6.12-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.12-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.12-1.4">lang-value<a href="#section-6.12-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.12-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.12-1.6">session, media<a href="#section-6.12-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.12-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.12-1.8">no<a href="#section-6.12-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.12-2">Syntax:<a href="#section-6.12-2" class="pilcrow">¶</a></p>
<div id="section-6.12-3">
<pre class="sourcecode lang-abnf">
      lang-value = Language-Tag
      ; Language-Tag defined in RFC 5646
</pre><a href="#section-6.12-3" class="pilcrow">¶</a>
</div>
<p id="section-6.12-4">Example:<a href="#section-6.12-4" class="pilcrow">¶</a></p>
<div id="section-6.12-5">
<pre class="sourcecode lang-sdp">
      a=lang:de
</pre><a href="#section-6.12-5" class="pilcrow">¶</a>
</div>
<p id="section-6.12-6">Multiple "a=lang:" attributes can be provided either at session or media
        level if the session or media has capabilities in more than one
        language, in which case the order of the attributes indicates the
        order of preference of the various languages in the session or media,
        from most preferred to least preferred.<a href="#section-6.12-6" class="pilcrow">¶</a></p>
<p id="section-6.12-7">As a session-level attribute, "a=lang:" specifies a language capability
        for the session being described. As a media-level attribute, it
        specifies a language capability for that media, overriding any
        session-level language(s) specified.<a href="#section-6.12-7" class="pilcrow">¶</a></p>
<p id="section-6.12-8">The "a=lang:" attribute value must be a single <span>[<a href="#RFC5646" class="xref">RFC5646</a>]</span> 
        language tag. An "a=lang:" attribute <span class="bcp14">SHOULD</span>
        be specified when a session is of sufficient scope to cross geographic
        boundaries where the language of participants cannot be assumed, or
        where the session has capabilities in languages different from the
        locally assumed norm.<a href="#section-6.12-8" class="pilcrow">¶</a></p>
<p id="section-6.12-9">The "a=lang:" attribute is supposed to be used for setting the initial
 language(s) used in the session. Events during the session may influence which language(s) are used, and the participants are not strictly bound to only use the declared languages.<a href="#section-6.12-9" class="pilcrow">¶</a></p>
<p id="section-6.12-10">Most real-time use cases start with just one language used, while other cases involve a range of languages, e.g., an interpreted or subtitled session. When more than one "a=lang:" attribute is specified, 
the "a=lang:" attribute itself does not provide any information about multiple languages being intended to be used during the session, or if the intention is to only select one of the languages. If needed, a new attribute can be defined and used to indicate such intentions. Without such semantics, it is assumed that for a negotiated session one of the declared languages will be selected and used.<a href="#section-6.12-10" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-6.13">
        <h3 id="name-framerate-frame-rate">
<a href="#section-6.13" class="section-number selfRef">6.13. </a><a href="#name-framerate-frame-rate" class="section-name selfRef">framerate (Frame Rate)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.13-1">
          <dt id="section-6.13-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.13-1.2">framerate<a href="#section-6.13-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.13-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.13-1.4">framerate-value<a href="#section-6.13-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.13-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.13-1.6">media<a href="#section-6.13-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.13-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.13-1.8">no<a href="#section-6.13-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.13-2">Syntax:<a href="#section-6.13-2" class="pilcrow">¶</a></p>
<div id="section-6.13-3">
<pre class="sourcecode lang-abnf">
      framerate-value = non-zero-int-or-real
</pre><a href="#section-6.13-3" class="pilcrow">¶</a>
</div>
<p id="section-6.13-4">Example:<a href="#section-6.13-4" class="pilcrow">¶</a></p>
<div id="section-6.13-5">
<pre class="sourcecode lang-sdp">
      a=framerate:60
</pre><a href="#section-6.13-5" class="pilcrow">¶</a>
</div>
<p id="section-6.13-6">This gives the maximum video frame rate in frames/sec. It is
        intended as a recommendation for the encoding of video data. Decimal
        representations of fractional values are allowed. It is defined only
        for video media.<a href="#section-6.13-6" class="pilcrow">¶</a></p>
</section>
<section id="section-6.14">
        <h3 id="name-quality">
<a href="#section-6.14" class="section-number selfRef">6.14. </a><a href="#name-quality" class="section-name selfRef">quality</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.14-1">
          <dt id="section-6.14-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.14-1.2">quality<a href="#section-6.14-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.14-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.14-1.4">quality-value<a href="#section-6.14-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.14-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.14-1.6">media<a href="#section-6.14-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.14-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.14-1.8">no<a href="#section-6.14-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.14-2">Syntax:<a href="#section-6.14-2" class="pilcrow">¶</a></p>
<div id="section-6.14-3">
<pre class="sourcecode lang-abnf">
      quality-value = zero-based-integer
</pre><a href="#section-6.14-3" class="pilcrow">¶</a>
</div>
<p id="section-6.14-4">Example:<a href="#section-6.14-4" class="pilcrow">¶</a></p>
<div id="section-6.14-5">
<pre class="sourcecode lang-sdp">
      a=quality:10
</pre><a href="#section-6.14-5" class="pilcrow">¶</a>
</div>
<p id="section-6.14-6">This gives a suggestion for the quality of the encoding as an
        integer value. The intention of the quality attribute for video is to
        specify a non-default trade-off between frame-rate and still-image
        quality. For video, the value is in the range 0 to 10, with the
        following suggested meaning:<a href="#section-6.14-6" class="pilcrow">¶</a></p>
<span id="name-encoding-quality-values"></span><table class="center" id="table-2">
          <caption>
<a href="#table-2" class="selfRef">Table 2</a>:
<a href="#name-encoding-quality-values" class="selfRef">Encoding Quality Values</a>
          </caption>
<tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">10</td>
              <td class="text-left" rowspan="1" colspan="1">the best still-image quality the compression scheme can give.</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">5</td>
              <td class="text-left" rowspan="1" colspan="1">the default behavior given no quality suggestion.</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">0</td>
              <td class="text-left" rowspan="1" colspan="1">the worst still-image quality the codec designer thinks is still usable.</td>
            </tr>
          </tbody>
        </table>
</section>
<div id="fmtp">
<section id="section-6.15">
        <h3 id="name-fmtp-format-parameters">
<a href="#section-6.15" class="section-number selfRef">6.15. </a><a href="#name-fmtp-format-parameters" class="section-name selfRef">fmtp (Format Parameters)</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.15-1">
          <dt id="section-6.15-1.1">Name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.15-1.2">fmtp<a href="#section-6.15-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.15-1.3">Value:</dt>
          <dd style="margin-left: 1.5em" id="section-6.15-1.4">fmtp-value<a href="#section-6.15-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.15-1.5">Usage Level:</dt>
          <dd style="margin-left: 1.5em" id="section-6.15-1.6">media<a href="#section-6.15-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.15-1.7">Charset Dependent:</dt>
          <dd style="margin-left: 1.5em" id="section-6.15-1.8">no<a href="#section-6.15-1.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-6.15-2">Syntax:<a href="#section-6.15-2" class="pilcrow">¶</a></p>
<div id="section-6.15-3">
<pre class="sourcecode lang-abnf">
      fmtp-value = fmt SP format-specific-params
      format-specific-params = byte-string
        ; Notes:
        ; - The format parameters are media type parameters and
        ;   need to reflect their syntax.
</pre><a href="#section-6.15-3" class="pilcrow">¶</a>
</div>
<p id="section-6.15-4">Example:<a href="#section-6.15-4" class="pilcrow">¶</a></p>
<div id="section-6.15-5">
<pre class="sourcecode lang-sdp">
      a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
</pre><a href="#section-6.15-5" class="pilcrow">¶</a>
</div>
<p id="section-6.15-6">This attribute allows parameters that are specific to a particular
        format to be conveyed in a way that SDP does not have to understand
        them. The format must be one of the formats specified for the media.
        Format-specific parameters, semicolon separated, may be any set of parameters required to be
        conveyed by SDP and given unchanged to the media tool that will use
        this format. At most one instance of this attribute is allowed for
        each format.<a href="#section-6.15-6" class="pilcrow">¶</a></p>
<p id="section-6.15-7">The "a=fmtp:" attribute may be used to specify parameters for any
        protocol and format that defines use of such parameters.<a href="#section-6.15-7" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="security">
<section id="section-7">
      <h2 id="name-security-considerations">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-7-1">SDP is frequently used with the <span><a href="#RFC3261" class="xref">Session
      Initiation Protocol</a> [<a href="#RFC3261" class="xref">RFC3261</a>]</span> using the <span><a href="#RFC3264" class="xref">offer/answer
      model</a> [<a href="#RFC3264" class="xref">RFC3264</a>]</span> to agree on parameters for unicast sessions. When used in
      this manner, the security considerations of those protocols apply.<a href="#section-7-1" class="pilcrow">¶</a></p>
<p id="section-7-2">SDP is a session description format that describes multimedia
      sessions. Entities receiving and acting upon an SDP message <span class="bcp14">SHOULD</span> be
      aware that a session description cannot be trusted unless it has been
      obtained by an authenticated and integrity-protected transport protocol from a known and trusted
      source. Many different transport protocols may be used to distribute
      session descriptions, and the nature of the authentication and integrity protection  will differ
      from transport to transport. For some transports, security features are
      often not deployed. In case a session description has not been obtained
      in a trusted manner, the endpoint <span class="bcp14">SHOULD</span> exercise care because, among
      other attacks, the media sessions received may not be the intended ones,
      the destination to where the media is sent  may not be the expected one, any
      of the parameters of the session may be incorrect, or the media security
      may be compromised. It is up to the endpoint to make a sensible decision,
      taking into account the security risks of the application and the user
      preferences - the endpoint may decide to ask the user whether or not to accept the
      session.<a href="#section-7-2" class="pilcrow">¶</a></p>
<p id="section-7-3">On receiving a session description over an unauthenticated transport
      mechanism or from an untrusted party, software parsing the session description
      should take a few precautions. Similar concerns apply if integrity protection is not in place. 
      Session descriptions contain information
      required to start software on the receiver's system. Software that
      parses a session description <span class="bcp14">MUST NOT</span> be able to start other software
      except that which is specifically configured as appropriate software to
      participate in multimedia sessions. It is normally considered
      inappropriate for software parsing a session description to start, on a
      user's system, software that is appropriate to participate in multimedia
      sessions, without the user first being informed that such software will
      be started and giving the user's consent. Thus, a session description
      arriving by session announcement, email, session invitation, or WWW page
      <span class="bcp14">MUST NOT</span> deliver the user into an interactive multimedia session unless
      the user has explicitly pre-authorized such action. As it is not always
      simple to tell whether or not a session is interactive, applications
      that are unsure should assume sessions are interactive.
      Software processing URLs contained in session descriptions should also 
      heed the security considerations identified in <span>[<a href="#RFC3986" class="xref">RFC3986</a>]</span>.<a href="#section-7-3" class="pilcrow">¶</a></p>
<p id="section-7-4">In this specification, there are no attributes that would allow the
      recipient of a session description to be informed to start multimedia
      tools in a mode where they default to transmitting. Under some
      circumstances it might be appropriate to define such attributes. If this
      is done, an application parsing a session description containing such
      attributes <span class="bcp14">SHOULD</span> either ignore them or inform the user that joining
      this session will result in the automatic transmission of multimedia
      data. The default behavior for an unknown attribute is to ignore
      it.<a href="#section-7-4" class="pilcrow">¶</a></p>
<p id="section-7-5">In certain environments, it has become common for intermediary
      systems to intercept and analyze session descriptions contained within
      other signaling protocols. This is done for a range of purposes,
      including but not limited to opening holes in firewalls to allow media
      streams to pass, or to mark, prioritize, or block traffic selectively.
      In some cases, such intermediary systems may modify the session
      description, for example, to have the contents of the session
      description match NAT bindings dynamically created. These behaviors are
      <span class="bcp14">NOT RECOMMENDED</span> unless the session description is conveyed in such a
      manner that allows the intermediary system to conduct proper checks to
      establish the authenticity of the session description, and the authority
      of its source to establish such communication sessions. SDP by itself
      does not include sufficient information to enable these checks: they
      depend on the encapsulating protocol (e.g., SIP or RTSP).
      The use of some procedures and SDP extensions 
      (e.g., Interactive Connectivity Establishment (ICE) <span>[<a href="#RFC8445" class="xref">RFC8445</a>]</span> 
      and ICE-SIP-SDP <span>[<a href="#RFC8839" class="xref">RFC8839</a>]</span>) 
      may avoid the need for intermediaries to modify SDP.<a href="#section-7-5" class="pilcrow">¶</a></p>
<p id="section-7-6">SDP <span class="bcp14">MUST NOT</span> be used to convey keying material (e.g., using 
      the "a=crypto:" attribute <span>[<a href="#RFC4568" class="xref">RFC4568</a>]</span>) unless it can be guaranteed that the channel over 
      which the SDP is delivered is both private and authenticated.<a href="#section-7-6" class="pilcrow">¶</a></p>
</section>
</div>
<div id="iana">
<section id="section-8">
      <h2 id="name-iana-considerations">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<section id="section-8.1">
        <h3 id="name-the-application-sdp-media-t">
<a href="#section-8.1" class="section-number selfRef">8.1. </a><a href="#name-the-application-sdp-media-t" class="section-name selfRef">The "application/sdp" Media Type</a>
        </h3>
<p id="section-8.1-1">One media type registration from <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span> has been 
        updated, as defined below.<a href="#section-8.1-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-8.1-2">
          <dt id="section-8.1-2.1">Type name:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.2">application<a href="#section-8.1-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.3">Subtype name:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.4">sdp<a href="#section-8.1-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.5">Required parameters:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.6">None.<a href="#section-8.1-2.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.7">Optional parameters:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.8">None.<a href="#section-8.1-2.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.9">Encoding considerations:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.10">8-bit text.
      SDP files are primarily UTF-8 format text. The "a=charset:"
      attribute may be used to signal the presence of other character
      sets in certain parts of an SDP file (see <a href="#attrs" class="xref">Section 6</a> of RFC
      8866).  Arbitrary binary content cannot be directly
      represented in SDP.<a href="#section-8.1-2.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.11">Security considerations:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.12">
      See <a href="#security" class="xref">Section 7</a> of RFC 8866.<a href="#section-8.1-2.12" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.13">Interoperability considerations:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.14">
      See RFC 8866.<a href="#section-8.1-2.14" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.15">Published specification:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.16">
      See RFC 8866.<a href="#section-8.1-2.16" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.17">Applications which use this media type:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.18">
            <p id="section-8.1-2.18.1"><br>
      Voice over IP, video teleconferencing, streaming media, instant
      messaging, among others.  See also <a href="#usage_examples" class="xref">Section 3</a> of RFC 8866.<a href="#section-8.1-2.18.1" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.19">Fragment identifier considerations:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.20">None<a href="#section-8.1-2.20" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.21">Additional information:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.22">
            <p id="section-8.1-2.22.1"><br></p>
<span class="break"></span><dl class="dlParallel dlCompact" id="section-8.1-2.22.2">
              <dt id="section-8.1-2.22.2.1">Deprecated alias names for this type:</dt>
              <dd style="margin-left: 1.5em" id="section-8.1-2.22.2.2">N/A<a href="#section-8.1-2.22.2.2" class="pilcrow">¶</a>
</dd>
              <dd class="break"></dd>
<dt id="section-8.1-2.22.2.3">Magic number(s):</dt>
              <dd style="margin-left: 1.5em" id="section-8.1-2.22.2.4">None.<a href="#section-8.1-2.22.2.4" class="pilcrow">¶</a>
</dd>
              <dd class="break"></dd>
<dt id="section-8.1-2.22.2.5">File extension(s):</dt>
              <dd style="margin-left: 1.5em" id="section-8.1-2.22.2.6">The extension ".sdp" is commonly used.<a href="#section-8.1-2.22.2.6" class="pilcrow">¶</a>
</dd>
              <dd class="break"></dd>
<dt id="section-8.1-2.22.2.7">Macintosh File Type Code(s):</dt>
              <dd style="margin-left: 1.5em" id="section-8.1-2.22.2.8">"sdp"<a href="#section-8.1-2.22.2.8" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
</dl>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.23">Person &amp; email address to contact for further information:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.24">
            <br>
      IETF MMUSIC working group<br>&lt;mmusic@ietf.org&gt;<a href="#section-8.1-2.24" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.25">Intended usage:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.26">COMMON<a href="#section-8.1-2.26" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.27">Restrictions on usage:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.28">None<a href="#section-8.1-2.28" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-2.29">Author/Change controller:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-2.30">
            <br>
      Authors of RFC 8866<br>
      IETF MMUSIC working group delegated from the IESG<a href="#section-8.1-2.30" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
<div id="SDP_Parameters">
<section id="section-8.2">
        <h3 id="name-registration-of-sdp-paramet">
<a href="#section-8.2" class="section-number selfRef">8.2. </a><a href="#name-registration-of-sdp-paramet" class="section-name selfRef">Registration of SDP Parameters with IANA</a>
        </h3>
<p id="section-8.2-1">This document specifies IANA parameter registries
        for six named SDP subfields. Using
        the terminology in the SDP specification Augmented Backus-Naur Form (ABNF), they
        are &lt;media&gt;, &lt;proto&gt;, &lt;attribute-name&gt;, &lt;bwtype&gt;, &lt;nettype&gt;, and
        &lt;addrtype&gt;.<a href="#section-8.2-1" class="pilcrow">¶</a></p>
<p id="section-8.2-2">This document also replaces and updates the definitions of all those parameters previously
        defined by <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span>.<a href="#section-8.2-2" class="pilcrow">¶</a></p>
<p id="section-8.2-3">IANA has changed all references to RFC 4566 in these registries to instead refer to this document.<a href="#section-8.2-3" class="pilcrow">¶</a></p>
<p id="section-8.2-4">The contact name and email address for all parameters registered in this document is:<a href="#section-8.2-4" class="pilcrow">¶</a></p>
<p style="margin-left: 1.5em" id="section-8.2-5">The IETF MMUSIC working group &lt;mmusic@ietf.org&gt; or its successor as designated by the IESG.<a href="#section-8.2-5" class="pilcrow">¶</a></p>
<p id="section-8.2-6">All of these registries have a common format:<a href="#section-8.2-6" class="pilcrow">¶</a></p>
<span id="name-common-format-for-sdp-regis"></span><table class="center" id="table-3">
          <caption>
<a href="#table-3" class="selfRef">Table 3</a>:
<a href="#name-common-format-for-sdp-regis" class="selfRef">Common Format for SDP Registries</a>
          </caption>
<tbody>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Type</th>
              <th class="text-left" rowspan="1" colspan="1">SDP Name</th>
              <th class="text-left" rowspan="1" colspan="1">[other fields]</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </tbody>
        </table>
<div id="Registration_Procedure">
<section id="section-8.2.1">
          <h4 id="name-registration-procedure">
<a href="#section-8.2.1" class="section-number selfRef">8.2.1. </a><a href="#name-registration-procedure" class="section-name selfRef">Registration Procedure</a>
          </h4>
<p id="section-8.2.1-1">A specification document that defines values for SDP &lt;media&gt;, &lt;proto&gt;, 
          &lt;attribute-name&gt;, &lt;bwtype&gt;, &lt;nettype&gt;, and &lt;addrtype&gt; parameters <span class="bcp14">MUST</span>
          include the following information:<a href="#section-8.2.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-8.2.1-2.1">Contact name<a href="#section-8.2.1-2.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-8.2.1-2.2">Contact email address<a href="#section-8.2.1-2.2" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-8.2.1-2.3">Name being defined (as it will appear in SDP)<a href="#section-8.2.1-2.3" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-8.2.1-2.4">Type of name (&lt;media&gt;, &lt;proto&gt;, &lt;attribute-name&gt;, &lt;bwtype&gt;, &lt;nettype&gt;,
              or &lt;addrtype&gt;)<a href="#section-8.2.1-2.4" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-8.2.1-2.5">A description of the purpose of the defined name<a href="#section-8.2.1-2.5" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-8.2.1-2.6">A stable reference to the document containing this
              information and the definition of the value.
              (This will typically be an RFC number.)<a href="#section-8.2.1-2.6" class="pilcrow">¶</a>
</li>
          </ul>
<p id="section-8.2.1-3">The subsections below specify what other information (if any) must be specified 
          for particular parameters, and what other fields are to be included 
          in the registry.<a href="#section-8.2.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="MediaTypes">
<section id="section-8.2.2">
          <h4 id="name-media-types-media">
<a href="#section-8.2.2" class="section-number selfRef">8.2.2. </a><a href="#name-media-types-media" class="section-name selfRef">Media Types (&lt;media&gt;)</a>
          </h4>
<p id="section-8.2.2-1">The set of media types is intended to be small and <span class="bcp14">SHOULD NOT</span> be
          extended except under rare circumstances. The same rules should
          apply for media names as well as for top-level media types, and where
          possible the same name should be registered for SDP as for MIME. For
          media other than existing top-level media types, a Standards Track
          RFC <span class="bcp14">MUST</span> be produced for a new top-level media type to be
          registered, and the registration <span class="bcp14">MUST</span> provide good justification why
          no existing media name is appropriate (the "Standards Action" policy
          of <span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span>).<a href="#section-8.2.2-1" class="pilcrow">¶</a></p>
<p id="section-8.2.2-2">This memo registers the media types "audio", "video", "text",
          "application", and "message".<a href="#section-8.2.2-2" class="pilcrow">¶</a></p>
<p id="section-8.2.2-3">Note: The media types "control" and "data" were listed as valid
          in an early version of this specification <span>[<a href="#RFC2327" class="xref">RFC2327</a>]</span>; however, their
          semantics were never fully specified, and they are not widely used.
          These media types have been removed in this specification, although
          they still remain valid media type capabilities for a SIP user agent
          as defined in <span>[<a href="#RFC3840" class="xref">RFC3840</a>]</span>. If these media types are
          considered useful in the future, a Standards Track RFC <span class="bcp14">MUST</span> be
          produced to document their use. Until that is done, applications
          <span class="bcp14">SHOULD NOT</span> use these types and <span class="bcp14">SHOULD NOT</span> declare support for them
          in SIP capabilities declarations (even though they exist in the
          registry created by <span>[<a href="#RFC3840" class="xref">RFC3840</a>]</span>). Also note that <span>[<a href="#RFC6466" class="xref">RFC6466</a>]</span> defined the "image" media type.<a href="#section-8.2.2-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="protoreg">
<section id="section-8.2.3">
          <h4 id="name-transport-protocols-proto">
<a href="#section-8.2.3" class="section-number selfRef">8.2.3. </a><a href="#name-transport-protocols-proto" class="section-name selfRef">Transport Protocols (&lt;proto&gt;)</a>
          </h4>
<p id="section-8.2.3-1">The &lt;proto&gt; subfield describes the transport protocol used.
          The registration procedure for this registry is "RFC Required".<a href="#section-8.2.3-1" class="pilcrow">¶</a></p>
<p id="section-8.2.3-2">This document registers two values:<a href="#section-8.2.3-2" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-8.2.3-3.1">"RTP/AVP" is a reference to <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span>
                   used under the <span><a href="#RFC3551" class="xref">RTP Profile for Audio and
                   Video Conferences with Minimal Control</a> [<a href="#RFC3551" class="xref">RFC3551</a>]</span> running over UDP/IP.<a href="#section-8.2.3-3.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-8.2.3-3.2">"udp" indicates direct use of UDP.<a href="#section-8.2.3-3.2" class="pilcrow">¶</a>
</li>
          </ul>
<p id="section-8.2.3-4">New transport protocols <span class="bcp14">MAY</span> be defined, and <span class="bcp14">MUST</span> be registered with IANA.
          Registrations <span class="bcp14">MUST</span> reference an RFC describing the protocol. Such an
          RFC <span class="bcp14">MAY</span> be Experimental or Informational, although it is preferable
          that it be Standards Track. The RFC defining a new protocol <span class="bcp14">MUST</span> define the rules
          by which the &lt;fmt&gt; (see below) namespace is managed.<a href="#section-8.2.3-4" class="pilcrow">¶</a></p>
<p id="section-8.2.3-5">&lt;proto&gt; names starting with "RTP/" <span class="bcp14">MUST</span> only be used for
          defining transport protocols that are profiles of RTP. 
          For example, a profile whose short name is "XYZ" would be denoted by 
          a &lt;proto&gt; subfield of "RTP/XYZ".<a href="#section-8.2.3-5" class="pilcrow">¶</a></p>
<p id="section-8.2.3-6">Each transport protocol, defined by the &lt;proto&gt; subfield, has an
          associated &lt;fmt&gt; namespace that describes the media formats that may
          be conveyed by that protocol. Formats cover all the possible
          encodings that could be transported in a multimedia session.<a href="#section-8.2.3-6" class="pilcrow">¶</a></p>
<p id="section-8.2.3-7">RTP payload formats under the "RTP/AVP" and other "RTP/*" profiles
          <span class="bcp14">MUST</span> use the payload type number as their &lt;fmt&gt; value. If the
          payload type number is dynamically assigned by this session
          description, an additional "a=rtpmap:" attribute <span class="bcp14">MUST</span> be included to
          specify the format name and parameters as defined by the media type
          registration for the payload format. It is <span class="bcp14">RECOMMENDED</span> that other
          RTP profiles that are registered (in combination with RTP) as SDP
          transport protocols specify the same rules for the &lt;fmt&gt;
          namespace.<a href="#section-8.2.3-7" class="pilcrow">¶</a></p>
<p id="section-8.2.3-8">For the "udp" protocol, the allowed &lt;fmt&gt; values are media subtypes
          from the IANA Media Types registry. The media type and subtype combination 
          &lt;media&gt;/&lt;fmt&gt; specifies the format of the body of UDP packets.
          Use of an existing media subtype for the format is encouraged. If no suitable media
          subtype exists, it is <span class="bcp14">RECOMMENDED</span> that a new one be registered
          through the IETF process <span>[<a href="#RFC6838" class="xref">RFC6838</a>]</span> by production of,
          or reference to, a Standards Track RFC that defines the format.<a href="#section-8.2.3-8" class="pilcrow">¶</a></p>
<p id="section-8.2.3-9">For other protocols, formats <span class="bcp14">MAY</span> be registered according to the
          rules of the associated &lt;proto&gt; specification.<a href="#section-8.2.3-9" class="pilcrow">¶</a></p>
<p id="section-8.2.3-10">Registrations of new formats <span class="bcp14">MUST</span> specify which transport
          protocols they apply to.<a href="#section-8.2.3-10" class="pilcrow">¶</a></p>
</section>
</div>
<div id="AttributeNames">
<section id="section-8.2.4">
          <h4 id="name-attribute-names-attribute-n">
<a href="#section-8.2.4" class="section-number selfRef">8.2.4. </a><a href="#name-attribute-names-attribute-n" class="section-name selfRef">Attribute Names (&lt;attribute-name&gt;)</a>
          </h4>
<p id="section-8.2.4-1">Attribute-field names (&lt;attribute-name&gt;) <span class="bcp14">MUST</span> be registered with
          IANA and documented to avoid any issues due to
          conflicting attribute definitions under the same name. 
          (While unknown attributes in
          SDP are simply ignored, conflicting ones that fragment the
          protocol are a serious problem.)<a href="#section-8.2.4-1" class="pilcrow">¶</a></p>
<p id="section-8.2.4-2">The format of the &lt;attribute-name&gt; registry is:<a href="#section-8.2.4-2" class="pilcrow">¶</a></p>
<span id="name-format-of-the-attribute-nam"></span><div id="attRegformat">
<table class="center" id="table-4">
            <caption>
<a href="#table-4" class="selfRef">Table 4</a>:
<a href="#name-format-of-the-attribute-nam" class="selfRef">Format of the &lt;attribute-name&gt; Registry</a>
            </caption>
<tbody>
              <tr>
                <th class="text-left" rowspan="1" colspan="1">Type</th>
                <th class="text-left" rowspan="1" colspan="1">SDP Name</th>
                <th class="text-left" rowspan="1" colspan="1">Usage Level</th>
                <th class="text-left" rowspan="1" colspan="1">Mux Category</th>
                <th class="text-left" rowspan="1" colspan="1">Reference</th>
              </tr>
            </tbody>
          </table>
</div>
<p id="section-8.2.4-4">For example, the attribute "a=lang:", which is defined for both
        session and media level, will be listed in the new registry as
        follows:<a href="#section-8.2.4-4" class="pilcrow">¶</a></p>
<span id="name-attribute-name-registry-exa"></span><div id="attReg">
<table class="center" id="table-5">
            <caption>
<a href="#table-5" class="selfRef">Table 5</a>:
<a href="#name-attribute-name-registry-exa" class="selfRef">&lt;attribute-name&gt; Registry Example</a>
            </caption>
<thead>
              <tr>
                <th class="text-left" rowspan="1" colspan="1">Type</th>
                <th class="text-left" rowspan="1" colspan="1">SDP Name</th>
                <th class="text-left" rowspan="1" colspan="1">Usage Level</th>
                <th class="text-left" rowspan="1" colspan="1">Mux Category</th>
                <th class="text-left" rowspan="1" colspan="1">Reference</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">attribute</td>
                <td class="text-left" rowspan="1" colspan="1">lang</td>
                <td class="text-left" rowspan="1" colspan="1">session, media</td>
                <td class="text-left" rowspan="1" colspan="1">TRANSPORT</td>
                <td class="text-left" rowspan="1" colspan="1">[RFC8866]
                     <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>
                </td>
              </tr>
            </tbody>
          </table>
</div>
<p id="section-8.2.4-6">This one &lt;attribute-name&gt; registry combines all of the previous usage-level-specific "att-field" 
          registries, including updates made by <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>,  
          and renames the "att-field" registry to the
          "attribute-name (formerly "att-field")" registry. 
          IANA has completed the necessary reformatting.<a href="#section-8.2.4-6" class="pilcrow">¶</a></p>
<p id="section-8.2.4-7"><a href="#attrs" class="xref">Section 6</a> of this document replaces the initial set of
          attribute definitions made by <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span>.
          IANA has updated the registry accordingly.<a href="#section-8.2.4-7" class="pilcrow">¶</a></p>
<p id="section-8.2.4-8">Documents can define new attributes and can also extend the
          definitions of previously defined attributes.<a href="#section-8.2.4-8" class="pilcrow">¶</a></p>
<div id="newatt">
<section id="section-8.2.4.1">
            <h5 id="name-new-attributes">
<a href="#section-8.2.4.1" class="section-number selfRef">8.2.4.1. </a><a href="#name-new-attributes" class="section-name selfRef">New Attributes</a>
            </h5>
<p id="section-8.2.4.1-1">New attribute registrations are accepted according to the
            "Specification Required" policy of <span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span>,
            provided that the specification includes the following
            information:<a href="#section-8.2.4.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-8.2.4.1-2.1">Contact name<a href="#section-8.2.4.1-2.1" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.2">Contact email address<a href="#section-8.2.4.1-2.2" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.3">Attribute name: the name of the attribute that will appear
                in SDP. This <span class="bcp14">MUST</span> conform to the definition of
                &lt;attribute-name&gt;.<a href="#section-8.2.4.1-2.3" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.4">Attribute syntax: for a value attribute (see <a href="#attribspec" class="xref">Section 5.13</a>),
                an ABNF definition of the attribute value &lt;attribute-value&gt;
                syntax (see <a href="#abnf" class="xref">Section 9</a>) <span class="bcp14">MUST</span> be provided.
                The syntax <span class="bcp14">MUST</span> follow the rule form per 
                <span><a href="https://www.rfc-editor.org/rfc/rfc5234#section-2.2" class="relref">Section 2.2</a> of [<a href="#RFC5234" class="xref">RFC5234</a>]</span> 
                and <span>[<a href="#RFC7405" class="xref">RFC7405</a>]</span>. This <span class="bcp14">SHALL</span> define the allowable
                values that the attribute might take. It <span class="bcp14">MAY</span> also define an
                extension method for the addition of future values. For a
                property attribute, the ABNF definition is omitted as the
                property attribute takes no values.<a href="#section-8.2.4.1-2.4" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.5">Attribute semantics: for a value attribute, a semantic
                description of the values that the attribute might take <span class="bcp14">MUST</span>
                be provided. The usage of a property attribute is described
                under Purpose below.<a href="#section-8.2.4.1-2.5" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.6">Attribute value: the name of an ABNF syntax rule defining
                the syntax of the value. Absence of a rule name indicates that
                the attribute takes no values. Enclosing the rule name in "["
                and "]" indicates that a value is optional.<a href="#section-8.2.4.1-2.6" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.7">Usage level: the usage level(s) of the attribute. 
                This <span class="bcp14">MUST</span> be one or more of the following: 
                session, media, source, dcsa, and dcsa(subprotocol). 
                For a definition of source-level attributes, see <span>[<a href="#RFC5576" class="xref">RFC5576</a>]</span>. 
                For a definition of dcsa attributes see
                <span>[<a href="#RFC8864" class="xref">RFC8864</a>]</span>.<a href="#section-8.2.4.1-2.7" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.8">Charset dependent: this <span class="bcp14">MUST</span> be "Yes" or "No" depending
                on whether the attribute value is subject to the "a=charset:" attribute.<a href="#section-8.2.4.1-2.8" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.9">Purpose: an explanation of the purpose and usage of the
                attribute.<a href="#section-8.2.4.1-2.9" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.10">O/A procedures: offer/answer procedures as explained in
                <span>[<a href="#RFC3264" class="xref">RFC3264</a>]</span>.<a href="#section-8.2.4.1-2.10" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.11">Mux Category: this <span class="bcp14">MUST</span> indicate one of the following
                categories: NORMAL, NOT RECOMMENDED, IDENTICAL, SUM, TRANSPORT,
                INHERIT, IDENTICAL-PER-PT, SPECIAL, or TBD as defined by
                <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>.<a href="#section-8.2.4.1-2.11" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.1-2.12">Reference: a reference to the specification defining the
                attribute.<a href="#section-8.2.4.1-2.12" class="pilcrow">¶</a>
</li>
            </ul>
<p id="section-8.2.4.1-3">The above is the minimum that IANA will accept. Attributes that
            are expected to see widespread use and interoperability <span class="bcp14">SHOULD</span> be
            documented with a Standards Track RFC that specifies the attribute
            more precisely.<a href="#section-8.2.4.1-3" class="pilcrow">¶</a></p>
<p id="section-8.2.4.1-4">Submitters of registrations should ensure that the
            specification is in the spirit of SDP attributes, most notably
            that the attribute is platform independent in the sense that it
            makes no implicit assumptions about operating systems and does not
            name specific pieces of software in a manner that might inhibit
            interoperability.<a href="#section-8.2.4.1-4" class="pilcrow">¶</a></p>
<p id="section-8.2.4.1-5">Submitters of registrations should also carefully choose the
            attribute usage level. They should not choose only "session" when
            the attribute can have different values when media is
            disaggregated, i.e., when each "m=" section has its own IP address
            on a different endpoint. In that case, the attribute type chosen
            should be "session, media" or "media" (depending on desired semantics). 
            The default rule is that for all new
            SDP attributes that can occur both in session and media level, the
            media level overrides the session level. When this is not the case
            for a new SDP attribute, it <span class="bcp14">MUST</span> be explicitly stated.<a href="#section-8.2.4.1-5" class="pilcrow">¶</a></p>
<p id="section-8.2.4.1-6">IANA has registered the initial set of attribute names
            (&lt;attribute-name&gt; values) with definitions as in <a href="#attrs" class="xref">Section 6</a> 
            of this memo (these definitions replace those in
            <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span>).<a href="#section-8.2.4.1-6" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-8.2.4.2">
            <h5 id="name-updates-to-existing-attribu">
<a href="#section-8.2.4.2" class="section-number selfRef">8.2.4.2. </a><a href="#name-updates-to-existing-attribu" class="section-name selfRef">Updates to Existing Attributes</a>
            </h5>
<p id="section-8.2.4.2-1">Updated attribute registrations are accepted according to the
            "Specification Required" policy of <span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span>.<a href="#section-8.2.4.2-1" class="pilcrow">¶</a></p>
<p id="section-8.2.4.2-2">The Designated Expert reviewing the update is requested to evaluate
            whether the update is compatible with the prior intent and use of the attribute,
            and whether the new document is of sufficient maturity and authority in
            relation to the prior document.<a href="#section-8.2.4.2-2" class="pilcrow">¶</a></p>
<p id="section-8.2.4.2-3">The specification updating the attribute (for
            example, by adding a new value) <span class="bcp14">MUST</span> update registration
            information items from  <a href="#newatt" class="xref">Section 8.2.4.1</a> according
            to the following constraints:<a href="#section-8.2.4.2-3" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-8.2.4.2-4.1">Contact name: a name for an entity 
                responsible for the update <span class="bcp14">MUST</span> be provided.<a href="#section-8.2.4.2-4.1" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.2">Contact email address: an email address for an entity 
                responsible for the update <span class="bcp14">MUST</span> be provided.<a href="#section-8.2.4.2-4.2" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.3">Attribute name: <span class="bcp14">MUST</span> be provided and <span class="bcp14">MUST NOT</span> be changed.
                Otherwise it is a new attribute.<a href="#section-8.2.4.2-4.3" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.4">Attribute syntax: the existing rule syntax with the syntax
                extensions <span class="bcp14">MUST</span> be provided if there is a change to the
                syntax. A revision to an existing attribute usage <span class="bcp14">MAY</span> extend
                the syntax of an attribute, but <span class="bcp14">MUST</span> be backward
                compatible.<a href="#section-8.2.4.2-4.4" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.5">Attribute semantics: a semantic description of new
                additional attribute values or a semantic extension of
                existing values. Existing attribute values semantics <span class="bcp14">MUST</span> only
                be extended in a backward compatible manner.<a href="#section-8.2.4.2-4.5" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.6">Usage level: updates <span class="bcp14">MAY</span> only add additional levels.<a href="#section-8.2.4.2-4.6" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.7">Charset dependent: <span class="bcp14">MUST NOT</span> be changed.<a href="#section-8.2.4.2-4.7" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.8">Purpose: <span class="bcp14">MAY</span> be extended according to the updated
                usage.<a href="#section-8.2.4.2-4.8" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.9">O/A procedures: <span class="bcp14">MAY</span> be updated in a backward compatible
                manner and/or it applies to a new usage level only.<a href="#section-8.2.4.2-4.9" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.10">Mux Category: no change unless from "TBD" to another value 
                (see <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>.
                It <span class="bcp14">MAY</span> also change if media level is being added to the
                definition of an attribute that previously did not include
                it.<a href="#section-8.2.4.2-4.10" class="pilcrow">¶</a>
</li>
              <li class="normal" id="section-8.2.4.2-4.11">Reference: a new (additional or replacement) reference <span class="bcp14">MUST</span> be provided.<a href="#section-8.2.4.2-4.11" class="pilcrow">¶</a>
</li>
            </ul>
<p id="section-8.2.4.2-5">Items <span class="bcp14">SHOULD</span> be omitted if there is no impact to them as a
            result of the attribute update.<a href="#section-8.2.4.2-5" class="pilcrow">¶</a></p>
</section>
</section>
</div>
<section id="section-8.2.5">
          <h4 id="name-bandwidth-specifiers-bwtype">
<a href="#section-8.2.5" class="section-number selfRef">8.2.5. </a><a href="#name-bandwidth-specifiers-bwtype" class="section-name selfRef">Bandwidth Specifiers (&lt;bwtype&gt;)</a>
          </h4>
<p id="section-8.2.5-1">A proliferation of bandwidth specifiers is strongly
          discouraged.<a href="#section-8.2.5-1" class="pilcrow">¶</a></p>
<p id="section-8.2.5-2">New bandwidth specifiers (&lt;bwtype&gt; subfield values) <span class="bcp14">MUST</span> be registered
          with IANA. The submission <span class="bcp14">MUST</span> reference a Standards Track RFC
          specifying the semantics of the bandwidth specifier precisely, and
          indicating when it should be used, and why the existing registered
          bandwidth specifiers do not suffice.<a href="#section-8.2.5-2" class="pilcrow">¶</a></p>
<p id="section-8.2.5-3">The RFC <span class="bcp14">MUST</span> specify the Mux Category for this value as defined by
          <span>[<a href="#RFC8859" class="xref">RFC8859</a>]</span>.<a href="#section-8.2.5-3" class="pilcrow">¶</a></p>
<p id="section-8.2.5-4">The format of the &lt;bwtype&gt; registry is:<a href="#section-8.2.5-4" class="pilcrow">¶</a></p>
<span id="name-format-of-the-bwtype-regist"></span><div id="bwtypeRegformat">
<table class="center" id="table-6">
            <caption>
<a href="#table-6" class="selfRef">Table 6</a>:
<a href="#name-format-of-the-bwtype-regist" class="selfRef">Format of the &lt;bwtype&gt; Registry</a>
            </caption>
<tbody>
              <tr>
                <th class="text-left" rowspan="1" colspan="1">Type</th>
                <th class="text-left" rowspan="1" colspan="1">SDP Name</th>
                <th class="text-left" rowspan="1" colspan="1">Mux Category</th>
                <th class="text-left" rowspan="1" colspan="1">Reference</th>
              </tr>
            </tbody>
          </table>
</div>
<p id="section-8.2.5-6">IANA has updated the &lt;bwtype&gt; registry entries for the 
          bandwidth specifiers "CT" and "AS" with the
          definitions in <a href="#bandwidthInfo" class="xref">Section 5.8</a> of this memo (these definitions replace
          those in <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span>).<a href="#section-8.2.5-6" class="pilcrow">¶</a></p>
</section>
<div id="nettypereg">
<section id="section-8.2.6">
          <h4 id="name-network-types-nettype">
<a href="#section-8.2.6" class="section-number selfRef">8.2.6. </a><a href="#name-network-types-nettype" class="section-name selfRef">Network Types (&lt;nettype&gt;)</a>
          </h4>
<p id="section-8.2.6-1">Network type "IN", representing the Internet, 
          is defined in <a href="#origin" class="xref">Section 5.2</a> and 
          <a href="#connection-information" class="xref">Section 5.7</a> of this memo
          (this definition replaces that in <span>[<a href="#RFC4566" class="xref">RFC4566</a>]</span>).<a href="#section-8.2.6-1" class="pilcrow">¶</a></p>
<p id="section-8.2.6-2">To enable SDP to reference a new non-Internet environment,
          a new network type (&lt;nettype&gt; subfield value) <span class="bcp14">MUST</span> be registered
          with IANA. The registration is subject to the "RFC Required" policy 
          of <span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span>. Although non-Internet environments are
          not normally the preserve of IANA, there may be circumstances when
          an Internet application needs to interoperate with a non-Internet
          application, such as when gatewaying an Internet telephone call into
          the Public Switched Telephone Network (PSTN). The number of network
          types should be small and should be rarely extended. A new network type
          registration <span class="bcp14">MUST</span> reference an RFC that gives details of the network
          type and the address type(s) that may be used with it.<a href="#section-8.2.6-2" class="pilcrow">¶</a></p>
<p id="section-8.2.6-3">The format of the &lt;nettype&gt; registry is:<a href="#section-8.2.6-3" class="pilcrow">¶</a></p>
<span id="name-format-of-the-nettype-regis"></span><div id="nettypeRegformat">
<table class="center" id="table-7">
            <caption>
<a href="#table-7" class="selfRef">Table 7</a>:
<a href="#name-format-of-the-nettype-regis" class="selfRef">Format of the &lt;nettype&gt; Registry</a>
            </caption>
<tbody>
              <tr>
                <th class="text-left" rowspan="1" colspan="1">Type</th>
                <th class="text-left" rowspan="1" colspan="1">SDP Name</th>
                <th class="text-left" rowspan="1" colspan="1">Usable addrtype Values</th>
                <th class="text-left" rowspan="1" colspan="1">Reference</th>
              </tr>
            </tbody>
          </table>
</div>
<p id="section-8.2.6-5">IANA has updated the &lt;nettype&gt; registry to this
        new format. The following is the updated content of the registry:<a href="#section-8.2.6-5" class="pilcrow">¶</a></p>
<span id="name-content-of-the-nettype-regi"></span><div id="nettypeReg">
<table class="center" id="table-8">
            <caption>
<a href="#table-8" class="selfRef">Table 8</a>:
<a href="#name-content-of-the-nettype-regi" class="selfRef">Content of the &lt;nettype&gt; registry</a>
            </caption>
<thead>
              <tr>
                <th class="text-left" rowspan="1" colspan="1">Type</th>
                <th class="text-left" rowspan="1" colspan="1">SDP Name</th>
                <th class="text-left" rowspan="1" colspan="1">Usable addrtype Values</th>
                <th class="text-left" rowspan="1" colspan="1">Reference</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">nettype</td>
                <td class="text-left" rowspan="1" colspan="1">IN</td>
                <td class="text-left" rowspan="1" colspan="1">IP4, IP6</td>
                <td class="text-left" rowspan="1" colspan="1">[RFC8866]</td>
              </tr>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">nettype</td>
                <td class="text-left" rowspan="1" colspan="1">TN</td>
                <td class="text-left" rowspan="1" colspan="1">RFC2543</td>
                <td class="text-left" rowspan="1" colspan="1">
                  <span>[<a href="#RFC2848" class="xref">RFC2848</a>]</span>
</td>
              </tr>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">nettype</td>
                <td class="text-left" rowspan="1" colspan="1">ATM</td>
                <td class="text-left" rowspan="1" colspan="1">NSAP, GWID, E164</td>
                <td class="text-left" rowspan="1" colspan="1">
                  <span>[<a href="#RFC3108" class="xref">RFC3108</a>]</span>
</td>
              </tr>
              <tr>
                <td class="text-left" rowspan="1" colspan="1">nettype</td>
                <td class="text-left" rowspan="1" colspan="1">PSTN</td>
                <td class="text-left" rowspan="1" colspan="1">E164</td>
                <td class="text-left" rowspan="1" colspan="1">
                  <span>[<a href="#RFC7195" class="xref">RFC7195</a>]</span>
</td>
              </tr>
            </tbody>
          </table>
</div>
<p id="section-8.2.6-7">Note that both <span>[<a href="#RFC7195" class="xref">RFC7195</a>]</span> 
          and <span>[<a href="#RFC3108" class="xref">RFC3108</a>]</span> registered "E164" as an
          address type, although <span>[<a href="#RFC7195" class="xref">RFC7195</a>]</span> mentions that the "E164" address type
          has a different context for ATM and PSTN networks.<a href="#section-8.2.6-7" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-8.2.7">
          <h4 id="name-address-types-addrtype">
<a href="#section-8.2.7" class="section-number selfRef">8.2.7. </a><a href="#name-address-types-addrtype" class="section-name selfRef">Address Types (&lt;addrtype&gt;)</a>
          </h4>
<p id="section-8.2.7-1">New address types (&lt;addrtype&gt;) <span class="bcp14">MUST</span> be registered with IANA. The
          registration is subject to the "RFC Required" policy
          of <span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span>. A new address type registration
          <span class="bcp14">MUST</span> reference an RFC, giving details of the syntax of the address
          type. Address types are not expected to be registered
          frequently.<a href="#section-8.2.7-1" class="pilcrow">¶</a></p>
<p id="section-8.2.7-2"><a href="#connection-information" class="xref">Section 5.7</a> of this document gives 
          new definitions of address types "IP4" and "IP6".<a href="#section-8.2.7-2" class="pilcrow">¶</a></p>
</section>
</section>
</div>
<section id="section-8.3">
        <h3 id="name-encryption-key-access-metho">
<a href="#section-8.3" class="section-number selfRef">8.3. </a><a href="#name-encryption-key-access-metho" class="section-name selfRef">Encryption Key Access Methods (OBSOLETE)</a>
        </h3>
<p id="section-8.3-1">The IANA previously maintained a table of SDP encryption key access
        method ("enckey") names. This table is obsolete, since the "k=" line
        is not extensible. New registrations <span class="bcp14">MUST NOT</span> be accepted.<a href="#section-8.3-1" class="pilcrow">¶</a></p>
</section>
</section>
</div>
<div id="abnf">
<section id="section-9">
      <h2 id="name-sdp-grammar">
<a href="#section-9" class="section-number selfRef">9. </a><a href="#name-sdp-grammar" class="section-name selfRef">SDP Grammar</a>
      </h2>
<p id="section-9-1">This section provides an Augmented BNF grammar for SDP. ABNF is
      defined in <span>[<a href="#RFC5234" class="xref">RFC5234</a>]</span> and <span>[<a href="#RFC7405" class="xref">RFC7405</a>]</span>.<a href="#section-9-1" class="pilcrow">¶</a></p>
<div id="section-9-2">
<pre class="sourcecode lang-abnf">
; SDP Syntax
session-description = version-field
                      origin-field
                      session-name-field
                      [information-field]
                      [uri-field]
                      *email-field
                      *phone-field
                      [connection-field]
                      *bandwidth-field
                      1*time-description
                      [key-field]
                      *attribute-field
                      *media-description

version-field =       %s"v" "=" 1*DIGIT CRLF
                          ;this memo describes version 0

origin-field =       %s"o" "=" username SP sess-id SP sess-version SP
                         nettype SP addrtype SP unicast-address CRLF

session-name-field =  %s"s" "=" text CRLF

information-field =   %s"i" "=" text CRLF

uri-field =           %s"u" "=" uri CRLF

email-field =         %s"e" "=" email-address CRLF

phone-field =         %s"p" "=" phone-number CRLF

connection-field =    %s"c" "=" nettype SP addrtype SP
                          connection-address CRLF
                          ;a connection field must be present
                          ;in every media description or at the
                          ;session level

bandwidth-field =     %s"b" "=" bwtype ":" bandwidth CRLF

time-description =    time-field
                          [repeat-description]

repeat-description =  1*repeat-field
                          [zone-field]

time-field =          %s"t" "=" start-time SP stop-time CRLF

repeat-field =        %s"r" "=" repeat-interval SP typed-time
                          1*(SP typed-time) CRLF

zone-field =          %s"z" "=" time SP ["-"] typed-time
                          *(SP time SP ["-"] typed-time) CRLF

key-field =           %s"k" "=" key-type CRLF

attribute-field =     %s"a" "=" attribute CRLF

media-description =   media-field
                      [information-field]
                      *connection-field
                      *bandwidth-field
                      [key-field]
                      *attribute-field

media-field =         %s"m" "=" media SP port ["/" integer]
                          SP proto 1*(SP fmt) CRLF

; sub-rules of 'o='
username =            non-ws-string
                      ;pretty wide definition, but doesn't
                      ;include space

sess-id =             1*DIGIT
                      ;should be unique for this username/host

sess-version =        1*DIGIT

nettype =             token
                      ;typically "IN"

addrtype =            token
                      ;typically "IP4" or "IP6"

; sub-rules of 'u='
uri =                 URI-reference
                      ; see RFC 3986

; sub-rules of 'e=', see RFC 5322 for definitions
email-address        = address-and-comment / dispname-and-address
                       / addr-spec
address-and-comment  = addr-spec 1*SP "(" 1*email-safe ")"
dispname-and-address = 1*email-safe 1*SP "&lt;" addr-spec "&gt;"

; sub-rules of 'p='
phone-number =        phone *SP "(" 1*email-safe ")" /
                      1*email-safe "&lt;" phone "&gt;" /
                      phone

phone =               ["+"] DIGIT 1*(SP / "-" / DIGIT)

; sub-rules of 'c='
connection-address =  multicast-address / unicast-address

; sub-rules of 'b='
bwtype =              token

bandwidth =           1*DIGIT

; sub-rules of 't='
start-time =          time / "0"

stop-time =           time / "0"

time =                POS-DIGIT 9*DIGIT
                      ; Decimal representation of time in
                      ; seconds since January 1, 1900 UTC.
                      ; The representation is an unbounded
                      ; length field containing at least
                      ; 10 digits. Unlike some representations
                      ; used elsewhere, time in SDP does not
                      ; wrap in the year 2036.

; sub-rules of 'r=' and 'z='
repeat-interval =     POS-DIGIT *DIGIT [fixed-len-time-unit]

typed-time =          1*DIGIT [fixed-len-time-unit]

fixed-len-time-unit = %s"d" / %s"h" / %s"m" / %s"s"
; NOTE: These units are case-sensitive.

; sub-rules of 'k='
key-type =            %s"prompt" /
                      %s"clear:" text /
                      %s"base64:" base64 /
                      %s"uri:" uri
                      ; NOTE: These names are case-sensitive.

base64      =         *base64-unit [base64-pad]
base64-unit =         4base64-char
base64-pad  =         2base64-char "==" / 3base64-char "="
base64-char =         ALPHA / DIGIT / "+" / "/"

; sub-rules of 'a='
attribute =           (attribute-name ":" attribute-value) /
                      attribute-name

attribute-name =      token

attribute-value =     byte-string

att-field =           attribute-name ; for backward compatibility

; sub-rules of 'm='
media =               token
                      ;typically "audio", "video", "text", "image"
                      ;or "application"

fmt =                 token
                      ;typically an RTP payload type for audio
                      ;and video media

proto  =              token *("/" token)
                      ;typically "RTP/AVP", "RTP/SAVP", "udp",
                      ;or "RTP/SAVPF"

port =                1*DIGIT

; generic sub-rules: addressing
unicast-address =     IP4-address / IP6-address / FQDN / extn-addr

multicast-address =   IP4-multicast / IP6-multicast / FQDN
                      / extn-addr

IP4-multicast =       m1 3( "." decimal-uchar )
                      "/" ttl [ "/" numaddr ]
                      ; IP4 multicast addresses may be in the
                      ; range 224.0.0.0 to 239.255.255.255

m1 =                  ("22" ("4"/"5"/"6"/"7"/"8"/"9")) /
                      ("23" DIGIT )

IP6-multicast =       IP6-address [ "/" numaddr ]
                      ; IP6 address starting with FF

numaddr =             integer

ttl =                 (POS-DIGIT *2DIGIT) / "0"

FQDN =                4*(alpha-numeric / "-" / ".")
                      ; fully qualified domain name as specified
                      ; in RFC 1035 (and updates)

IP4-address =         b1 3("." decimal-uchar)

b1 =                  decimal-uchar
                      ; less than "224"

IP6-address =                                      6( h16 ":" ) ls32
                      /                       "::" 5( h16 ":" ) ls32
                      / [               h16 ] "::" 4( h16 ":" ) ls32
                      / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
                      / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
                      / [ *3( h16 ":" ) h16 ] "::"    h16 ":"   ls32
                      / [ *4( h16 ":" ) h16 ] "::"              ls32
                      / [ *5( h16 ":" ) h16 ] "::"              h16
                      / [ *6( h16 ":" ) h16 ] "::"

h16 =                 1*4HEXDIG

ls32 =                ( h16 ":" h16 ) / IP4-address

; Generic for other address families
extn-addr =      non-ws-string

; generic sub-rules: datatypes
text =                byte-string
                      ;default is to interpret this as UTF8 text.
                      ;ISO 8859-1 requires "a=charset:ISO-8859-1"
                      ;session-level attribute to be used

byte-string =         1*(%x01-09/%x0B-0C/%x0E-FF)
                      ;any byte except NUL, CR, or LF

non-ws-string =       1*(VCHAR/%x80-FF)
                      ;string of visible characters

token-char =          ALPHA / DIGIT
                              / "!" / "#" / "$" / "%" / "&amp;"
                              / "'" ; (single quote)
                              / "*" / "+" / "-" / "." / "^" / "_"
                              / "`" ; (Grave accent)
                              / "{" / "|" / "}" / "~"

token =               1*(token-char)

email-safe =          %x01-09/%x0B-0C/%x0E-27/%x2A-3B/%x3D/%x3F-FF
                      ;any byte except NUL, CR, LF, or the quoting
                      ;characters ()&lt;&gt;

integer =             POS-DIGIT *DIGIT

zero-based-integer = "0" / integer

non-zero-int-or-real = integer / non-zero-real

non-zero-real = zero-based-integer "." *DIGIT POS-DIGIT

; generic sub-rules: primitives
alpha-numeric =       ALPHA / DIGIT

POS-DIGIT =           %x31-39 ; 1 - 9

decimal-uchar =       DIGIT
                      / POS-DIGIT DIGIT
                      / ("1" 2(DIGIT))
                      / ("2" ("0"/"1"/"2"/"3"/"4") DIGIT)
                      / ("2" "5" ("0"/"1"/"2"/"3"/"4"/"5"))

; external references:
ALPHA =               &lt;ALPHA definition from RFC 5234&gt;
DIGIT =               &lt;DIGIT definition from RFC 5234&gt;
CRLF =                &lt;CRLF definition from RFC 5234&gt;
HEXDIG =              &lt;HEXDIG definition from RFC 5234&gt;
SP =                  &lt;SP definition from RFC 5234&gt;
VCHAR =               &lt;VCHAR definition from RFC 5234&gt;
URI-reference =       &lt;URI-reference definition from RFC 3986&gt;
addr-spec =           &lt;addr-spec definition from RFC 5322&gt;
</pre><a href="#section-9-2" class="pilcrow">¶</a>
</div>
</section>
</div>
<div id="changes">
<section id="section-10">
      <h2 id="name-summary-of-changes-from-rfc">
<a href="#section-10" class="section-number selfRef">10. </a><a href="#name-summary-of-changes-from-rfc" class="section-name selfRef">Summary of Changes from RFC 4566</a>
      </h2>
<ul class="normal">
<li class="normal" id="section-10-1.1">Generally clarified and refined terminology. Aligned terms used in
   text with the ABNF. The terms &lt;attribute&gt;, &lt;att-field&gt;, and
   "att-field" are now &lt;attribute-name&gt;. The terms &lt;value&gt; and
   &lt;att-value&gt; are now &lt;attribute-value&gt;. The term "media" is now
   &lt;media&gt;.<a href="#section-10-1.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.2">Identified now-obsolete items: "a=cat:" (<a href="#cat" class="xref">Section 6.1</a>), 
            "a=keywds:" (<a href="#keywds" class="xref">Section 6.2</a>), and "k=" 
            (<a href="#key-field" class="xref">Section 5.12</a>).<a href="#section-10-1.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.3">Updated normative and informative references, and added references 
        to additional relevant related RFCs.<a href="#section-10-1.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.4">Reformatted the SDP Attributes section (<a href="#attrs" class="xref">Section 6</a>) for readability. 
        The syntax of attribute values is now given in ABNF.<a href="#section-10-1.4" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.5">Made mandatory the sending of RTCP with inactive media streams (<a href="#inactive" class="xref">Section 6.7.4</a>).<a href="#section-10-1.5" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.6">Removed the section "Private Sessions". That section dated back to a time
     when the primary use of SDP was with SAP (Session Announcement Protocol),
     which has fallen out of use. Now the vast majority of uses of SDP is
     for establishment of private sessions. The considerations for that are
     covered in <a href="#security" class="xref">Section 7</a>.<a href="#section-10-1.6" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.7">Expanded and clarified the specification of the "a=lang:" (<a href="#lang" class="xref">Section 6.12</a>) 
        and "a=sdplang:" (<a href="#sdplang" class="xref">Section 6.11</a>) attributes.<a href="#section-10-1.7" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.8">Removed some references to SAP because it is no longer in widespread use.<a href="#section-10-1.8" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.9">Changed the way &lt;fmt&gt; values for UDP transport are registered (<a href="#protoreg" class="xref">Section 8.2.3</a>).<a href="#section-10-1.9" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.10">Changed the mechanism and documentation required for 
        registering new attributes (<a href="#newatt" class="xref">Section 8.2.4.1</a>).<a href="#section-10-1.10" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.11">Tightened up IANA registration procedures for extensions. 
        Removed phone number and long-form name (<a href="#SDP_Parameters" class="xref">Section 8.2</a>).<a href="#section-10-1.11" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.12">Expanded the IANA &lt;nettype&gt; registry to identify valid &lt;addrtype&gt; subfields (<a href="#nettypereg" class="xref">Section 8.2.6</a>).<a href="#section-10-1.12" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.13">Reorganized the several IANA "att-field" registries 
        into a single &lt;attribute-name&gt; registry (<a href="#AttributeNames" class="xref">Section 8.2.4</a>).<a href="#section-10-1.13" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.14">
          <p id="section-10-1.14.1">Revised ABNF syntax (<a href="#abnf" class="xref">Section 9</a>) for clarity
                   and for alignment with text. Backward compatibility is 
                   maintained with a few exceptions.  Of particular note:<a href="#section-10-1.14.1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-10-1.14.2.1">Revised the syntax of time descriptions ("t=", "r=", "z=") to 
               remove ambiguities. Clarified that "z=" only modifies the 
               immediately preceding "r=" lines. Made "z=" without a 
        preceding "r=" a syntax error (<a href="#tzadj" class="xref">Section 5.11</a>). 
        (This is incompatible with certain aberrant usage.)<a href="#section-10-1.14.2.1" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-10-1.14.2.2">Updated the "IP6-address" and "IP6-multicast" rules, consistent 
               with the syntax in <span>[<a href="#RFC3986" class="xref">RFC3986</a>]</span>, mirroring a bug fix made to 
               <span>[<a href="#RFC3261" class="xref">RFC3261</a>]</span> by <span>[<a href="#RFC5954" class="xref">RFC5954</a>]</span>. 
        Removed rules that were unused as a result of this change.<a href="#section-10-1.14.2.2" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-10-1.14.2.3">The "att-field" rule has been renamed "attribute-name" because
               elsewhere "*-field" always refers to a complete line. However,
               the rulename "att-field" remains defined as a synonym for
               backward compatibility with references from other RFCs.<a href="#section-10-1.14.2.3" class="pilcrow">¶</a>
</li>
            <li class="normal" id="section-10-1.14.2.4">The "att-value" rule has been renamed "attribute-value".<a href="#section-10-1.14.2.4" class="pilcrow">¶</a>
</li>
          </ul>
</li>
        <li class="normal" id="section-10-1.15">Revised normative statements that were redundant with ABNF syntax,
            making the text non-normative.<a href="#section-10-1.15" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.16">Revised IPv4 unicast and multicast addresses in the 
        example SDP descriptions per <span>[<a href="#RFC5735" class="xref">RFC5735</a>]</span> and <span>[<a href="#RFC5771" class="xref">RFC5771</a>]</span>.<a href="#section-10-1.16" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.17">Changed some examples to use IPv6 addresses, and added additional
            examples using IPv6.<a href="#section-10-1.17" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.18">Incorporated case-insensitivity rules from <span>[<a href="#RFC4855" class="xref">RFC4855</a>]</span>.<a href="#section-10-1.18" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.19">Revised sections that incorrectly referenced NTP (<a href="#origin" class="xref">Section 5.2</a>, 
            <a href="#timing" class="xref">Section 5.9</a>, <a href="#repeattime" class="xref">Section 5.10</a>, and 
            <a href="#tzadj" class="xref">Section 5.11</a>).<a href="#section-10-1.19" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.20">Clarified the explanation of the impact and use of the "a=charset:" attribute
            (<a href="#charset" class="xref">Section 6.10</a>).<a href="#section-10-1.20" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-10-1.21">Revised the description of the "a=type:" attribute to remove implication that it
            sometimes changes the default media direction to something other than "a=sendrecv"
            (<a href="#type" class="xref">Section 6.9</a>).<a href="#section-10-1.21" class="pilcrow">¶</a>
</li>
      </ul>
</section>
</div>
<section id="section-11">
      <h2 id="name-references">
<a href="#section-11" class="section-number selfRef">11. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-11.1">
        <h3 id="name-normative-references">
<a href="#section-11.1" class="section-number selfRef">11.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="E164">[E164]</dt>
        <dd>
<span class="refAuthor">International Telecommunication Union</span>, <span class="refTitle">"E.164 : The international public telecommunication numbering plan"</span>, <span class="seriesInfo">ITU Recommendation E.164</span>, <time datetime="2010-11" class="refDate">November 2010</time>, <span>&lt;<a href="https://www.itu.int/rec/T-REC-E.164-201011-I/en">https://www.itu.int/rec/T-REC-E.164-201011-I/en</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="ISO.8859-1.1998">[ISO.8859-1.1998]</dt>
        <dd>
<span class="refAuthor">International Organization for Standardization</span>, <span class="refTitle">"Information technology - 8-bit single byte coded graphic - character sets - Part 1: Latin alphabet No. 1, JTC1/SC2"</span>, <span class="seriesInfo">ISO/IEC Standard 8859-1</span>, <time datetime="1998" class="refDate">1998</time>. </dd>
<dd class="break"></dd>
<dt id="RFC1034">[RFC1034]</dt>
        <dd>
<span class="refAuthor">Mockapetris, P.</span>, <span class="refTitle">"Domain names - concepts and facilities"</span>, <span class="seriesInfo">STD 13</span>, <span class="seriesInfo">RFC 1034</span>, <span class="seriesInfo">DOI 10.17487/RFC1034</span>, <time datetime="1987-11" class="refDate">November 1987</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc1034">https://www.rfc-editor.org/info/rfc1034</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC1035">[RFC1035]</dt>
        <dd>
<span class="refAuthor">Mockapetris, P.</span>, <span class="refTitle">"Domain names - implementation and specification"</span>, <span class="seriesInfo">STD 13</span>, <span class="seriesInfo">RFC 1035</span>, <span class="seriesInfo">DOI 10.17487/RFC1035</span>, <time datetime="1987-11" class="refDate">November 1987</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc1035">https://www.rfc-editor.org/info/rfc1035</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2119">[RFC2119]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03" class="refDate">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2848">[RFC2848]</dt>
        <dd>
<span class="refAuthor">Petrack, S.</span><span class="refAuthor"> and L. Conroy</span>, <span class="refTitle">"The PINT Service Protocol: Extensions to SIP and SDP for IP Access to Telephone Call Services"</span>, <span class="seriesInfo">RFC 2848</span>, <span class="seriesInfo">DOI 10.17487/RFC2848</span>, <time datetime="2000-06" class="refDate">June 2000</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2848">https://www.rfc-editor.org/info/rfc2848</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2978">[RFC2978]</dt>
        <dd>
<span class="refAuthor">Freed, N.</span><span class="refAuthor"> and J. Postel</span>, <span class="refTitle">"IANA Charset Registration Procedures"</span>, <span class="seriesInfo">BCP 19</span>, <span class="seriesInfo">RFC 2978</span>, <span class="seriesInfo">DOI 10.17487/RFC2978</span>, <time datetime="2000-10" class="refDate">October 2000</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2978">https://www.rfc-editor.org/info/rfc2978</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3108">[RFC3108]</dt>
        <dd>
<span class="refAuthor">Kumar, R.</span><span class="refAuthor"> and M. Mostafa</span>, <span class="refTitle">"Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections"</span>, <span class="seriesInfo">RFC 3108</span>, <span class="seriesInfo">DOI 10.17487/RFC3108</span>, <time datetime="2001-05" class="refDate">May 2001</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3108">https://www.rfc-editor.org/info/rfc3108</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3629">[RFC3629]</dt>
        <dd>
<span class="refAuthor">Yergeau, F.</span>, <span class="refTitle">"UTF-8, a transformation format of ISO 10646"</span>, <span class="seriesInfo">STD 63</span>, <span class="seriesInfo">RFC 3629</span>, <span class="seriesInfo">DOI 10.17487/RFC3629</span>, <time datetime="2003-11" class="refDate">November 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3629">https://www.rfc-editor.org/info/rfc3629</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3986">[RFC3986]</dt>
        <dd>
<span class="refAuthor">Berners-Lee, T.</span><span class="refAuthor">, Fielding, R.</span><span class="refAuthor">, and L. Masinter</span>, <span class="refTitle">"Uniform Resource Identifier (URI): Generic Syntax"</span>, <span class="seriesInfo">STD 66</span>, <span class="seriesInfo">RFC 3986</span>, <span class="seriesInfo">DOI 10.17487/RFC3986</span>, <time datetime="2005-01" class="refDate">January 2005</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3986">https://www.rfc-editor.org/info/rfc3986</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4566">[RFC4566]</dt>
        <dd>
<span class="refAuthor">Handley, M.</span><span class="refAuthor">, Jacobson, V.</span><span class="refAuthor">, and C. Perkins</span>, <span class="refTitle">"SDP: Session Description Protocol"</span>, <span class="seriesInfo">RFC 4566</span>, <span class="seriesInfo">DOI 10.17487/RFC4566</span>, <time datetime="2006-07" class="refDate">July 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4566">https://www.rfc-editor.org/info/rfc4566</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5234">[RFC5234]</dt>
        <dd>
<span class="refAuthor">Crocker, D., Ed.</span><span class="refAuthor"> and P. Overell</span>, <span class="refTitle">"Augmented BNF for Syntax Specifications: ABNF"</span>, <span class="seriesInfo">STD 68</span>, <span class="seriesInfo">RFC 5234</span>, <span class="seriesInfo">DOI 10.17487/RFC5234</span>, <time datetime="2008-01" class="refDate">January 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5234">https://www.rfc-editor.org/info/rfc5234</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5576">[RFC5576]</dt>
        <dd>
<span class="refAuthor">Lennox, J.</span><span class="refAuthor">, Ott, J.</span><span class="refAuthor">, and T. Schierl</span>, <span class="refTitle">"Source-Specific Media Attributes in the Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 5576</span>, <span class="seriesInfo">DOI 10.17487/RFC5576</span>, <time datetime="2009-06" class="refDate">June 2009</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5576">https://www.rfc-editor.org/info/rfc5576</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5646">[RFC5646]</dt>
        <dd>
<span class="refAuthor">Phillips, A., Ed.</span><span class="refAuthor"> and M. Davis, Ed.</span>, <span class="refTitle">"Tags for Identifying Languages"</span>, <span class="seriesInfo">BCP 47</span>, <span class="seriesInfo">RFC 5646</span>, <span class="seriesInfo">DOI 10.17487/RFC5646</span>, <time datetime="2009-09" class="refDate">September 2009</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5646">https://www.rfc-editor.org/info/rfc5646</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5890">[RFC5890]</dt>
        <dd>
<span class="refAuthor">Klensin, J.</span>, <span class="refTitle">"Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework"</span>, <span class="seriesInfo">RFC 5890</span>, <span class="seriesInfo">DOI 10.17487/RFC5890</span>, <time datetime="2010-08" class="refDate">August 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5890">https://www.rfc-editor.org/info/rfc5890</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5952">[RFC5952]</dt>
        <dd>
<span class="refAuthor">Kawamura, S.</span><span class="refAuthor"> and M. Kawashima</span>, <span class="refTitle">"A Recommendation for IPv6 Address Text Representation"</span>, <span class="seriesInfo">RFC 5952</span>, <span class="seriesInfo">DOI 10.17487/RFC5952</span>, <time datetime="2010-08" class="refDate">August 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5952">https://www.rfc-editor.org/info/rfc5952</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7195">[RFC7195]</dt>
        <dd>
<span class="refAuthor">Garcia-Martin, M.</span><span class="refAuthor"> and S. Veikkolainen</span>, <span class="refTitle">"Session Description Protocol (SDP) Extension for Setting Audio and Video Media Streams over Circuit-Switched Bearers in the Public Switched Telephone Network (PSTN)"</span>, <span class="seriesInfo">RFC 7195</span>, <span class="seriesInfo">DOI 10.17487/RFC7195</span>, <time datetime="2014-05" class="refDate">May 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7195">https://www.rfc-editor.org/info/rfc7195</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8126">[RFC8126]</dt>
        <dd>
<span class="refAuthor">Cotton, M.</span><span class="refAuthor">, Leiba, B.</span><span class="refAuthor">, and T. Narten</span>, <span class="refTitle">"Guidelines for Writing an IANA Considerations Section in RFCs"</span>, <span class="seriesInfo">BCP 26</span>, <span class="seriesInfo">RFC 8126</span>, <span class="seriesInfo">DOI 10.17487/RFC8126</span>, <time datetime="2017-06" class="refDate">June 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8126">https://www.rfc-editor.org/info/rfc8126</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8174">[RFC8174]</dt>
        <dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05" class="refDate">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8859">[RFC8859]</dt>
        <dd>
<span class="refAuthor">Nandakumar, S.</span>, <span class="refTitle">"A Framework for Session Description Protocol (SDP) Attributes When Multiplexing"</span>, <span class="seriesInfo">RFC 8859</span>, <span class="seriesInfo">DOI 10.17487/RFC8859</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8859">https://www.rfc-editor.org/info/rfc8859</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8864">[RFC8864]</dt>
      <dd>
<span class="refAuthor">Drage, K.</span><span class="refAuthor">, Makaraju, M.</span><span class="refAuthor">, Ejzak, R.</span><span class="refAuthor">, Marcon, J.</span><span class="refAuthor">, and R. Even, Ed.</span>, <span class="refTitle">"Negotiation Data Channels Using the Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 8864</span>, <span class="seriesInfo">DOI 10.17487/RFC8864</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8864">https://www.rfc-editor.org/info/rfc8864</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-11.2">
        <h3 id="name-informative-references">
<a href="#section-11.2" class="section-number selfRef">11.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="ITU.H332.1998">[ITU.H332.1998]</dt>
        <dd>
<span class="refAuthor">International Telecommunication Union</span>, <span class="refTitle">"H.332 : H.323 extended for loosely coupled conferences"</span>, <span class="seriesInfo">ITU Recommendation H.332</span>, <time datetime="1998-09" class="refDate">September 1998</time>, <span>&lt;<a href="https://www.itu.int/rec/T-REC-H.332-199809-I/en">https://www.itu.int/rec/T-REC-H.332-199809-I/en</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2045">[RFC2045]</dt>
        <dd>
<span class="refAuthor">Freed, N.</span><span class="refAuthor"> and N. Borenstein</span>, <span class="refTitle">"Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"</span>, <span class="seriesInfo">RFC 2045</span>, <span class="seriesInfo">DOI 10.17487/RFC2045</span>, <time datetime="1996-11" class="refDate">November 1996</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2045">https://www.rfc-editor.org/info/rfc2045</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2327">[RFC2327]</dt>
        <dd>
<span class="refAuthor">Handley, M.</span><span class="refAuthor"> and V. Jacobson</span>, <span class="refTitle">"SDP: Session Description Protocol"</span>, <span class="seriesInfo">RFC 2327</span>, <span class="seriesInfo">DOI 10.17487/RFC2327</span>, <time datetime="1998-04" class="refDate">April 1998</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2327">https://www.rfc-editor.org/info/rfc2327</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2974">[RFC2974]</dt>
        <dd>
<span class="refAuthor">Handley, M.</span><span class="refAuthor">, Perkins, C.</span><span class="refAuthor">, and E. Whelan</span>, <span class="refTitle">"Session Announcement Protocol"</span>, <span class="seriesInfo">RFC 2974</span>, <span class="seriesInfo">DOI 10.17487/RFC2974</span>, <time datetime="2000-10" class="refDate">October 2000</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2974">https://www.rfc-editor.org/info/rfc2974</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3261">[RFC3261]</dt>
        <dd>
<span class="refAuthor">Rosenberg, J.</span><span class="refAuthor">, Schulzrinne, H.</span><span class="refAuthor">, Camarillo, G.</span><span class="refAuthor">, Johnston, A.</span><span class="refAuthor">, Peterson, J.</span><span class="refAuthor">, Sparks, R.</span><span class="refAuthor">, Handley, M.</span><span class="refAuthor">, and E. Schooler</span>, <span class="refTitle">"SIP: Session Initiation Protocol"</span>, <span class="seriesInfo">RFC 3261</span>, <span class="seriesInfo">DOI 10.17487/RFC3261</span>, <time datetime="2002-06" class="refDate">June 2002</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3261">https://www.rfc-editor.org/info/rfc3261</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3264">[RFC3264]</dt>
        <dd>
<span class="refAuthor">Rosenberg, J.</span><span class="refAuthor"> and H. Schulzrinne</span>, <span class="refTitle">"An Offer/Answer Model with Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 3264</span>, <span class="seriesInfo">DOI 10.17487/RFC3264</span>, <time datetime="2002-06" class="refDate">June 2002</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3264">https://www.rfc-editor.org/info/rfc3264</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3550">[RFC3550]</dt>
        <dd>
<span class="refAuthor">Schulzrinne, H.</span><span class="refAuthor">, Casner, S.</span><span class="refAuthor">, Frederick, R.</span><span class="refAuthor">, and V. Jacobson</span>, <span class="refTitle">"RTP: A Transport Protocol for Real-Time Applications"</span>, <span class="seriesInfo">STD 64</span>, <span class="seriesInfo">RFC 3550</span>, <span class="seriesInfo">DOI 10.17487/RFC3550</span>, <time datetime="2003-07" class="refDate">July 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3550">https://www.rfc-editor.org/info/rfc3550</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3551">[RFC3551]</dt>
        <dd>
<span class="refAuthor">Schulzrinne, H.</span><span class="refAuthor"> and S. Casner</span>, <span class="refTitle">"RTP Profile for Audio and Video Conferences with Minimal Control"</span>, <span class="seriesInfo">STD 65</span>, <span class="seriesInfo">RFC 3551</span>, <span class="seriesInfo">DOI 10.17487/RFC3551</span>, <time datetime="2003-07" class="refDate">July 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3551">https://www.rfc-editor.org/info/rfc3551</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3556">[RFC3556]</dt>
        <dd>
<span class="refAuthor">Casner, S.</span>, <span class="refTitle">"Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth"</span>, <span class="seriesInfo">RFC 3556</span>, <span class="seriesInfo">DOI 10.17487/RFC3556</span>, <time datetime="2003-07" class="refDate">July 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3556">https://www.rfc-editor.org/info/rfc3556</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3605">[RFC3605]</dt>
        <dd>
<span class="refAuthor">Huitema, C.</span>, <span class="refTitle">"Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 3605</span>, <span class="seriesInfo">DOI 10.17487/RFC3605</span>, <time datetime="2003-10" class="refDate">October 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3605">https://www.rfc-editor.org/info/rfc3605</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3711">[RFC3711]</dt>
        <dd>
<span class="refAuthor">Baugher, M.</span><span class="refAuthor">, McGrew, D.</span><span class="refAuthor">, Naslund, M.</span><span class="refAuthor">, Carrara, E.</span><span class="refAuthor">, and K. Norrman</span>, <span class="refTitle">"The Secure Real-time Transport Protocol (SRTP)"</span>, <span class="seriesInfo">RFC 3711</span>, <span class="seriesInfo">DOI 10.17487/RFC3711</span>, <time datetime="2004-03" class="refDate">March 2004</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3711">https://www.rfc-editor.org/info/rfc3711</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3840">[RFC3840]</dt>
        <dd>
<span class="refAuthor">Rosenberg, J.</span><span class="refAuthor">, Schulzrinne, H.</span><span class="refAuthor">, and P. Kyzivat</span>, <span class="refTitle">"Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)"</span>, <span class="seriesInfo">RFC 3840</span>, <span class="seriesInfo">DOI 10.17487/RFC3840</span>, <time datetime="2004-08" class="refDate">August 2004</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3840">https://www.rfc-editor.org/info/rfc3840</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3890">[RFC3890]</dt>
        <dd>
<span class="refAuthor">Westerlund, M.</span>, <span class="refTitle">"A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 3890</span>, <span class="seriesInfo">DOI 10.17487/RFC3890</span>, <time datetime="2004-09" class="refDate">September 2004</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3890">https://www.rfc-editor.org/info/rfc3890</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4568">[RFC4568]</dt>
        <dd>
<span class="refAuthor">Andreasen, F.</span><span class="refAuthor">, Baugher, M.</span><span class="refAuthor">, and D. Wing</span>, <span class="refTitle">"Session Description Protocol (SDP) Security Descriptions for Media Streams"</span>, <span class="seriesInfo">RFC 4568</span>, <span class="seriesInfo">DOI 10.17487/RFC4568</span>, <time datetime="2006-07" class="refDate">July 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4568">https://www.rfc-editor.org/info/rfc4568</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4855">[RFC4855]</dt>
        <dd>
<span class="refAuthor">Casner, S.</span>, <span class="refTitle">"Media Type Registration of RTP Payload Formats"</span>, <span class="seriesInfo">RFC 4855</span>, <span class="seriesInfo">DOI 10.17487/RFC4855</span>, <time datetime="2007-02" class="refDate">February 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4855">https://www.rfc-editor.org/info/rfc4855</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5124">[RFC5124]</dt>
        <dd>
<span class="refAuthor">Ott, J.</span><span class="refAuthor"> and E. Carrara</span>, <span class="refTitle">"Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)"</span>, <span class="seriesInfo">RFC 5124</span>, <span class="seriesInfo">DOI 10.17487/RFC5124</span>, <time datetime="2008-02" class="refDate">February 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5124">https://www.rfc-editor.org/info/rfc5124</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5322">[RFC5322]</dt>
        <dd>
<span class="refAuthor">Resnick, P., Ed.</span>, <span class="refTitle">"Internet Message Format"</span>, <span class="seriesInfo">RFC 5322</span>, <span class="seriesInfo">DOI 10.17487/RFC5322</span>, <time datetime="2008-10" class="refDate">October 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5322">https://www.rfc-editor.org/info/rfc5322</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5735">[RFC5735]</dt>
        <dd>
<span class="refAuthor">Cotton, M.</span><span class="refAuthor"> and L. Vegoda</span>, <span class="refTitle">"Special Use IPv4 Addresses"</span>, <span class="seriesInfo">RFC 5735</span>, <span class="seriesInfo">DOI 10.17487/RFC5735</span>, <time datetime="2010-01" class="refDate">January 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5735">https://www.rfc-editor.org/info/rfc5735</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5771">[RFC5771]</dt>
        <dd>
<span class="refAuthor">Cotton, M.</span><span class="refAuthor">, Vegoda, L.</span><span class="refAuthor">, and D. Meyer</span>, <span class="refTitle">"IANA Guidelines for IPv4 Multicast Address Assignments"</span>, <span class="seriesInfo">BCP 51</span>, <span class="seriesInfo">RFC 5771</span>, <span class="seriesInfo">DOI 10.17487/RFC5771</span>, <time datetime="2010-03" class="refDate">March 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5771">https://www.rfc-editor.org/info/rfc5771</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5888">[RFC5888]</dt>
        <dd>
<span class="refAuthor">Camarillo, G.</span><span class="refAuthor"> and H. Schulzrinne</span>, <span class="refTitle">"The Session Description Protocol (SDP) Grouping Framework"</span>, <span class="seriesInfo">RFC 5888</span>, <span class="seriesInfo">DOI 10.17487/RFC5888</span>, <time datetime="2010-06" class="refDate">June 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5888">https://www.rfc-editor.org/info/rfc5888</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5954">[RFC5954]</dt>
        <dd>
<span class="refAuthor">Gurbani, V., Ed.</span><span class="refAuthor">, Carpenter, B., Ed.</span><span class="refAuthor">, and B. Tate, Ed.</span>, <span class="refTitle">"Essential Correction for IPv6 ABNF and URI Comparison in RFC 3261"</span>, <span class="seriesInfo">RFC 5954</span>, <span class="seriesInfo">DOI 10.17487/RFC5954</span>, <time datetime="2010-08" class="refDate">August 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5954">https://www.rfc-editor.org/info/rfc5954</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6466">[RFC6466]</dt>
        <dd>
<span class="refAuthor">Salgueiro, G.</span>, <span class="refTitle">"IANA Registration of the 'image' Media Type for the Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 6466</span>, <span class="seriesInfo">DOI 10.17487/RFC6466</span>, <time datetime="2011-12" class="refDate">December 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6466">https://www.rfc-editor.org/info/rfc6466</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6838">[RFC6838]</dt>
        <dd>
<span class="refAuthor">Freed, N.</span><span class="refAuthor">, Klensin, J.</span><span class="refAuthor">, and T. Hansen</span>, <span class="refTitle">"Media Type Specifications and Registration Procedures"</span>, <span class="seriesInfo">BCP 13</span>, <span class="seriesInfo">RFC 6838</span>, <span class="seriesInfo">DOI 10.17487/RFC6838</span>, <time datetime="2013-01" class="refDate">January 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6838">https://www.rfc-editor.org/info/rfc6838</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7230">[RFC7230]</dt>
        <dd>
<span class="refAuthor">Fielding, R., Ed.</span><span class="refAuthor"> and J. Reschke, Ed.</span>, <span class="refTitle">"Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing"</span>, <span class="seriesInfo">RFC 7230</span>, <span class="seriesInfo">DOI 10.17487/RFC7230</span>, <time datetime="2014-06" class="refDate">June 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7230">https://www.rfc-editor.org/info/rfc7230</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7405">[RFC7405]</dt>
        <dd>
<span class="refAuthor">Kyzivat, P.</span>, <span class="refTitle">"Case-Sensitive String Support in ABNF"</span>, <span class="seriesInfo">RFC 7405</span>, <span class="seriesInfo">DOI 10.17487/RFC7405</span>, <time datetime="2014-12" class="refDate">December 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7405">https://www.rfc-editor.org/info/rfc7405</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7656">[RFC7656]</dt>
        <dd>
<span class="refAuthor">Lennox, J.</span><span class="refAuthor">, Gross, K.</span><span class="refAuthor">, Nandakumar, S.</span><span class="refAuthor">, Salgueiro, G.</span><span class="refAuthor">, and B. Burman, Ed.</span>, <span class="refTitle">"A Taxonomy of Semantics and Mechanisms for Real-Time Transport Protocol (RTP) Sources"</span>, <span class="seriesInfo">RFC 7656</span>, <span class="seriesInfo">DOI 10.17487/RFC7656</span>, <time datetime="2015-11" class="refDate">November 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7656">https://www.rfc-editor.org/info/rfc7656</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7826">[RFC7826]</dt>
        <dd>
<span class="refAuthor">Schulzrinne, H.</span><span class="refAuthor">, Rao, A.</span><span class="refAuthor">, Lanphier, R.</span><span class="refAuthor">, Westerlund, M.</span><span class="refAuthor">, and M. Stiemerling, Ed.</span>, <span class="refTitle">"Real-Time Streaming Protocol Version 2.0"</span>, <span class="seriesInfo">RFC 7826</span>, <span class="seriesInfo">DOI 10.17487/RFC7826</span>, <time datetime="2016-12" class="refDate">December 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7826">https://www.rfc-editor.org/info/rfc7826</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8445">[RFC8445]</dt>
        <dd>
<span class="refAuthor">Keranen, A.</span><span class="refAuthor">, Holmberg, C.</span><span class="refAuthor">, and J. Rosenberg</span>, <span class="refTitle">"Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal"</span>, <span class="seriesInfo">RFC 8445</span>, <span class="seriesInfo">DOI 10.17487/RFC8445</span>, <time datetime="2018-07" class="refDate">July 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8445">https://www.rfc-editor.org/info/rfc8445</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8839">[RFC8839]</dt>
        <dd>
<span class="refAuthor">Petit-Huguenin, M.</span><span class="refAuthor">, Nandakumar, S.</span><span class="refAuthor">, Holmberg, C.</span><span class="refAuthor">, Keränen, A.</span><span class="refAuthor">, and R. Shpount</span>, <span class="refTitle">"Session Description Protocol (SDP) Offer/Answer Procedures for Interactive Connectivity Establishment (ICE)"</span>, <span class="seriesInfo">RFC 8839</span>, <span class="seriesInfo">DOI 10.17487/RFC8839</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8839">https://www.rfc-editor.org/info/rfc8839</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8843">[RFC8843]</dt>
      <dd>
<span class="refAuthor">Holmberg, C.</span><span class="refAuthor">, Alvestrand, H.</span><span class="refAuthor">, and C. Jennings</span>, <span class="refTitle">"Negotiating Media Multiplexing Using the Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 8843</span>, <span class="seriesInfo">DOI 10.17487/RFC8843</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8843">https://www.rfc-editor.org/info/rfc8843</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<section id="section-appendix.a">
      <h2 id="name-acknowledgements">
<a href="#name-acknowledgements" class="section-name selfRef">Acknowledgements</a>
      </h2>
<p id="section-appendix.a-1">Many people in the IETF Multiparty Multimedia Session Control
      (MMUSIC) working group have made comments and suggestions contributing
      to this document.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
<p id="section-appendix.a-2">In particular, we would like to thank the following people who contributed 
      to the creation of this document or one of its predecessor documents:
      <span class="contact-name">Adam Roach</span>, <span class="contact-name">Allison Mankin</span>, 
      <span class="contact-name">Bernie Hoeneisen</span>, <span class="contact-name">Bill Fenner</span>, 
      <span class="contact-name">Carsten Bormann</span>, <span class="contact-name">Eve Schooler</span>, 
      <span class="contact-name">Flemming Andreasen</span>, <span class="contact-name">Gonzalo Camarillo</span>, 
      <span class="contact-name">Jörg Ott</span>, <span class="contact-name">John Elwell</span>, 
      <span class="contact-name">Jon Peterson</span>, <span class="contact-name">Jonathan Lennox</span>, 
      <span class="contact-name">Jonathan Rosenberg</span>, <span class="contact-name">Keith Drage</span>, 
      <span class="contact-name">Peter Parnes</span>, <span class="contact-name">Rob Lanphier</span>, 
      <span class="contact-name">Ross Finlayson</span>, <span class="contact-name">Sean Olson</span>, 
      <span class="contact-name">Spencer Dawkins</span>, <span class="contact-name">Steve Casner</span>, 
      <span class="contact-name">Steve Hanna</span>, <span class="contact-name">Van Jacobson</span>.<a href="#section-appendix.a-2" class="pilcrow">¶</a></p>
</section>
<div id="authors-addresses">
<section id="section-appendix.b">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Ali Begen</span></div>
<div dir="auto" class="left"><span class="org">Networked Media</span></div>
<div dir="auto" class="left"><span class="country-name">Turkey</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:ali.begen@networked.media" class="email">ali.begen@networked.media</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Paul Kyzivat</span></div>
<div dir="auto" class="left"><span class="country-name">United States of America</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:pkyzivat@alum.mit.edu" class="email">pkyzivat@alum.mit.edu</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Colin Perkins</span></div>
<div dir="auto" class="left"><span class="org">University of Glasgow</span></div>
<div dir="auto" class="left"><span class="extended-address">School of Computing Science</span></div>
<div dir="auto" class="left"><span class="locality">Glasgow</span></div>
<div dir="auto" class="left"><span class="postal-code">G12 8QQ</span></div>
<div dir="auto" class="left"><span class="country-name">United Kingdom</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:csp@csperkins.org" class="email">csp@csperkins.org</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Mark Handley</span></div>
<div dir="auto" class="left"><span class="org">University College London</span></div>
<div dir="auto" class="left"><span class="street-address">Department of Computer Science</span></div>
<div dir="auto" class="left"><span class="locality">London</span></div>
<div dir="auto" class="left"><span class="postal-code">WC1E 6BT</span></div>
<div dir="auto" class="left"><span class="country-name">United Kingdom</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:M.Handley@cs.ucl.ac.uk" class="email">M.Handley@cs.ucl.ac.uk</a>
</div>
</address>
</section>
</div>
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